diff --git a/.editorconfig b/.editorconfig
index 167b4f18..0818506d 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -12,7 +12,7 @@ indent_style = tab
 [*.{py,toml}]
 indent_size = 4
 
-[*.{json,xml,yaml,yml}]
+[*.{json,yaml,yml}]
 indent_size = 2
 
 [*.{rst,inc}]
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
index 390001de..0f9a1ce6 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -1,26 +1,32 @@
 ---
 name: Bug report
 about: Create a report to help us improve
-title: "[BUG] "
-labels: bug
+title: ""
+labels: Bug
 assignees: ""
 ---
 
-**Describe the bug** A clear and concise description of what the bug is.
+## Bug description
 
-**To Reproduce** Steps to reproduce the behavior:
+<!-- A clear and concise description of what the bug is. -->
+
+<!-- If applicable, add a log or screenshot to help explain your problem. -->
+
+## How to reproduce?
+
+Steps to reproduce the behavior:
 
 1.
 
-**Expected behavior** A clear and concise description of what you expected to
-happen.
+## Expected behavior
 
-**Error log** If applicable, add an error log or screenshots to help explain
-your problem.
+<!-- A clear and concise description of what you expected to happen. -->
 
-**Desktop (please complete the following information):**
+## System info
 
-- OS: [e.g. iOS]
-- Version [e.g. 22]
+Bug resulted on the following system:
 
-**Additional context** Add any other context about the problem here.
+- OS: <!-- e.g. macOS, WSL Ubuntu, ...-->
+- Version <!-- e.g. 10.15, 20.04, ... -->
+- Python version: <!-- e.g. 3.6, 3.7, ... -->
+- Virtual environment: <!-- e.g. venv, Conda, pip user install, ... -->
diff --git a/.github/ISSUE_TEMPLATE/feature_request.md b/.github/ISSUE_TEMPLATE/feature_request.md
index e10461af..af1efda5 100644
--- a/.github/ISSUE_TEMPLATE/feature_request.md
+++ b/.github/ISSUE_TEMPLATE/feature_request.md
@@ -1,20 +1,22 @@
 ---
 name: Feature request
 about: Suggest an idea for this project
-title: "[REQUEST] "
-labels: ""
+title: ""
+labels: "💡 Enhancement"
 assignees: ""
 ---
 
-**Is your feature request related to a problem? Please describe.** A clear and
+## Problem description
+
+<!-- Is your feature request related to a problem? Please provide a clear and
 concise description of what the problem is. [Example: "I'm always frustrated
-when ..."]
+when ..." -->
+
+## Proposed solution
 
-**Describe the solution you'd like** A clear and concise description of what
-you want to happen.
+<!-- Describe the solution you'd want to happen. -->
 
-**Describe alternatives you've considered** A clear and concise description of
-any alternative solutions or features you've considered.
+<!-- Are there alternatives you have considered? -->
 
-**Additional context** Add any other context or screenshots about the feature
-request here.
+<!-- Additional context: -->
+<!-- Add any other context or screenshots about the feature -->
diff --git a/.github/release-drafter.yml b/.github/release-drafter.yml
index 9c7f8d57..03c4d3d2 100644
--- a/.github/release-drafter.yml
+++ b/.github/release-drafter.yml
@@ -11,7 +11,8 @@ categories:
   - title: 🔨 Internals
     labels:
       - 🖱️ DX
-      - 💡 Enhancement
+      - 💡 Feature
+      - ⚠️ Interface
       - 🔨 Maintenance
 
 change-template: "- $TITLE (#$NUMBER)"
diff --git a/.github/workflows/cd.yml b/.github/workflows/cd.yml
index 3111ec71..73c2aff0 100644
--- a/.github/workflows/cd.yml
+++ b/.github/workflows/cd.yml
@@ -9,58 +9,10 @@ on:
       - released
 
 jobs:
-  documentation:
-    name: Build documentation and run notebooks
-    if: startsWith(github.ref, 'refs/tags')
-    runs-on: ubuntu-18.04
-    steps:
-      - uses: actions/checkout@v2
-      - name: Set up Python 3.7
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.7
-      - name: Install dependencies
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r .reqs/doc.txt
-          pip install .
-          sudo apt-get -y install pandoc graphviz
-      - name: Build documentation and run notebooks
-        working-directory: docs
-        env:
-          EXECUTE_NB: YES
-        run: make html
-      - name: Test doctests in docstrings
-        working-directory: docs
-        run: make ignore-warnings=1 doctest
-
-  style:
-    name: Style checks
-    if: startsWith(github.ref, 'refs/tags')
-    runs-on: ubuntu-18.04
-    steps:
-      - uses: actions/checkout@v2
-      - name: Set up Python 3.7
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.7
-      - name: Install dependencies
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r .reqs/sty.txt
-          pip install .
-          sudo npm install -g cspell pyright
-      - name: Perform style checks
-        run: pre-commit run -a
-      - name: Check spelling
-        run: cspell $(git ls-files)
-      - name: Run pyright
-        run: pyright
-
   push:
     name: Push to stable branch
     if: startsWith(github.ref, 'refs/tags')
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     needs:
       - documentation
       - style
diff --git a/.github/workflows/ci-epic.yml b/.github/workflows/ci-epic.yml
index eb7717bf..b7383111 100644
--- a/.github/workflows/ci-epic.yml
+++ b/.github/workflows/ci-epic.yml
@@ -13,7 +13,7 @@ on:
 jobs:
   documentation:
     name: Build documentation and run notebooks
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.7
@@ -32,7 +32,7 @@ jobs:
 
   style:
     name: Style checks
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.7
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 54f4b2ad..c85c9cd1 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,7 +17,7 @@ jobs:
   documentation:
     name: Build documentation and run notebooks
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.7
@@ -27,7 +27,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r .reqs/doc.txt
+          pip install -r reqs/3.7/requirements-doc.txt
           pip install .
           sudo apt-get -y install pandoc graphviz
       - name: Build documentation and run notebooks
@@ -37,7 +37,7 @@ jobs:
   style:
     name: Style checks
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.7
@@ -47,12 +47,12 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r .reqs/sty.txt
+          pip install -r reqs/3.7/requirements-sty.txt
           pip install .
           sudo npm install -g cspell pyright
       - name: Perform style checks
         run: pre-commit run -a
       - name: Check spelling
-        run: cspell $(git ls-files)
+        run: cspell --no-progress $(git ls-files)
       - name: Run pyright
         run: pyright
diff --git a/.github/workflows/linkcheck.yml b/.github/workflows/linkcheck.yml
index a977faa5..6022f494 100644
--- a/.github/workflows/linkcheck.yml
+++ b/.github/workflows/linkcheck.yml
@@ -17,7 +17,7 @@ jobs:
   check_links:
     name: Check external links
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.7
@@ -27,7 +27,8 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r .reqs/doc.txt
+          pip install -r reqs/3.7/requirements-doc.txt
+          pip install .
           sudo apt-get -y install pandoc
       - name: Check external links
         working-directory: docs
diff --git a/.github/workflows/pr-linting.yml b/.github/workflows/pr-linting.yml
index 2a168425..b4b709c3 100644
--- a/.github/workflows/pr-linting.yml
+++ b/.github/workflows/pr-linting.yml
@@ -14,19 +14,19 @@ on:
 jobs:
   check-labels:
     name: Check labels
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: docker://agilepathway/pull-request-label-checker:latest
         with:
           any_of: |
-            Bug,💡 Enhancement,📝 Docs,🔨 Maintenance,🖱️ DX,📖 Analysis,
+            Bug,💡 Feature,⚠️ Interface,📝 Docs,🔨 Maintenance,🖱️ DX,📖 Analysis,
             📖 Software,📖 Theory
           none_of: ❌ Won't fix,💫 Good first issue
           repo_token: ${{ secrets.GITHUB_TOKEN }}
 
   check-title:
     name: Check title
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v1
       - name: Install Dependencies
diff --git a/.github/workflows/release-drafter.yml b/.github/workflows/release-drafter.yml
index 17fdb961..a3373592 100644
--- a/.github/workflows/release-drafter.yml
+++ b/.github/workflows/release-drafter.yml
@@ -7,7 +7,7 @@ on:
 
 jobs:
   update_release_draft:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: release-drafter/release-drafter@v5
         env:
diff --git a/.github/workflows/requirements-cron.yml b/.github/workflows/requirements-cron.yml
new file mode 100644
index 00000000..1f6b89e4
--- /dev/null
+++ b/.github/workflows/requirements-cron.yml
@@ -0,0 +1,65 @@
+# cspell:ignore noreply
+
+name: Requirements (scheduled)
+
+on:
+  schedule:
+    - cron: "0 2 * * 1"
+
+jobs:
+  upgrade:
+    name: Upgrade requirement files
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version:
+          - 3.6
+          - 3.7
+          - 3.8
+          - 3.9
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@master
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pip-tools
+      - name: Upgrade dependencies
+        run: bash reqs/upgrade.sh
+      - uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.python-version }}
+          path: reqs/${{ matrix.python-version }}
+
+  push:
+    name: Create PR
+    runs-on: ubuntu-20.04
+    needs:
+      - upgrade
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          token: ${{ secrets.PAT }}
+      - uses: actions/download-artifact@v2
+        with:
+          path: reqs
+      - run: git status -s
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v3
+        with:
+          commit-message: "ci: upgrade developer dependencies"
+          committer: GitHub <noreply@github.com>
+          author: GitHub <noreply@github.com>
+          title: "ci: upgrade developer dependencies"
+          labels: |
+            🖱️ DX
+          branch-suffix: timestamp
+          delete-branch: true
+          token: ${{ secrets.PAT }}
+      - name: Print PR info
+        run: |
+          echo "Pull Request Number - ${{ steps.cpr.outputs.pull-request-number }}"
+          echo "Pull Request URL - ${{ steps.cpr.outputs.pull-request-url }}"
diff --git a/.github/workflows/requirements-pr.yml b/.github/workflows/requirements-pr.yml
new file mode 100644
index 00000000..4d2acc23
--- /dev/null
+++ b/.github/workflows/requirements-pr.yml
@@ -0,0 +1,90 @@
+# cspell:ignore noreply
+
+name: Requirements (PR)
+
+on:
+  pull_request:
+    branches: [master]
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - ready_for_review
+
+jobs:
+  upgrade:
+    name: Upgrade requirement files
+    if: github.event.pull_request.draft == false
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version:
+          - 3.6
+          - 3.7
+          - 3.8
+          - 3.9
+    steps:
+      - uses: actions/checkout@v2
+      - run: git fetch origin
+      - name: Check for modified dependencies
+        id: git-diff
+        run:
+          echo "::set-output name=dependency-changes::$(git diff
+          origin/$GITHUB_BASE_REF --name-only -- reqs setup.cfg)"
+        # Also triggers on (unwanted) changes to requirements.txt files
+      - name: Show dependency changes changes
+        run:
+          git diff origin/$GITHUB_BASE_REF -- reqs/requirements*.in setup.cfg
+      - name: Abort if fork PR and dependency changes
+        if:
+          github.event.pull_request.head.repo.full_name != github.repository &&
+          steps.git-diff.outputs.dependency-changes != ''
+        run: |
+          echo "::error::Cannot modify package dependencies through a PR from a fork"
+          exit 1
+      - name: Set up Python ${{ matrix.python-version }}
+        if: steps.git-diff.outputs.dependency-changes != ''
+        uses: actions/setup-python@master
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        if: steps.git-diff.outputs.dependency-changes != ''
+        run: |
+          python -m pip install --upgrade pip
+          pip install pip-tools
+      - name: Upgrade dependencies
+        if: steps.git-diff.outputs.dependency-changes != ''
+        run: bash reqs/upgrade.sh
+      - uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.python-version }}
+          path: reqs/${{ matrix.python-version }}
+
+  push:
+    name: Push changes
+    if: github.event.pull_request.draft == false
+    runs-on: ubuntu-20.04
+    needs:
+      - upgrade
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          token: ${{ secrets.PAT }}
+      - uses: actions/download-artifact@v2
+        with:
+          path: reqs
+      - run: git status -s
+      - name: Commit and push changes
+        run: |
+          git remote set-url origin https://x-access-token:${{ secrets.PAT }}@github.com/${{ github.repository }}
+          git config --global user.name ${{ github.actor }}
+          git config --global user.email "${{ github.actor }}@users.noreply.github.com"
+          git checkout -b ${GITHUB_HEAD_REF}
+          FILES_TO_COMMIT="reqs/*/requirements*.txt"
+          if [[ $(git diff -- ${FILES_TO_COMMIT}) ]]; then
+            git add ${FILES_TO_COMMIT}
+            git commit -m "ci: upgrade developer dependencies (automatic)"
+            git config pull.rebase true
+            git pull origin ${GITHUB_HEAD_REF}
+            git push origin HEAD:${GITHUB_HEAD_REF}
+          fi
diff --git a/.gitpod.yml b/.gitpod.yml
index 07a5d734..8a5d12f3 100644
--- a/.gitpod.yml
+++ b/.gitpod.yml
@@ -1,5 +1,5 @@
 tasks:
-  - init: pip install -r requirements-dev.txt -e .
+  - init: pip install -r reqs/3.8/requirements-dev.txt -e .
 
 github:
   prebuilds:
diff --git a/.readthedocs.yml b/.readthedocs.yml
index 46bbaa14..88f0b24f 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -9,8 +9,8 @@ formats:
   - htmlzip
 
 python:
-  version: 3.7
+  version: 3.8
   install:
-    - requirements: .reqs/doc.txt
+    - requirements: reqs/3.8/requirements-doc.txt
     - method: pip
       path: .
diff --git a/.reqs/dev.in b/.reqs/dev.in
deleted file mode 100644
index 2559c9ce..00000000
--- a/.reqs/dev.in
+++ /dev/null
@@ -1,9 +0,0 @@
--r ../requirements.txt
--r doc.txt
--r sty.txt
-
-jupyterlab
-jupyterlab-code-formatter
-labels
-pip-tools
-tox >= 1.9  # for skip_install, use_develop
diff --git a/.reqs/doc.txt b/.reqs/doc.txt
deleted file mode 100644
index 40d6eab4..00000000
--- a/.reqs/doc.txt
+++ /dev/null
@@ -1,117 +0,0 @@
-#
-# This file is autogenerated by pip-compile
-# To update, run:
-#
-#    pip-compile .reqs/doc.in
-#
-alabaster==0.7.12         # via sphinx
-argon2-cffi==20.1.0       # via notebook
-async-generator==1.10     # via nbclient
-attrs==20.3.0             # via jsonschema, jupyter-cache, markdown-it-py
-babel==2.9.0              # via sphinx
-backcall==0.2.0           # via ipython
-beautifulsoup4==4.9.3     # via sphinx-book-theme
-bleach==3.2.1             # via nbconvert
-certifi==2020.11.8        # via requests
-cffi==1.14.4              # via argon2-cffi
-chardet==3.0.4            # via requests
-click==7.1.2              # via sphinx-book-theme
-colorama==0.4.4           # via nbdime
-cycler==0.10.0            # via -r .reqs/../requirements.txt, matplotlib
-decorator==4.4.2          # via ipython
-defusedxml==0.6.0         # via nbconvert
-docutils==0.16            # via myst-nb, myst-parser, pybtex-docutils, sphinx, sphinx-book-theme, sphinx-panels, sphinx-togglebutton
-entrypoints==0.3          # via nbconvert
-gitdb==4.0.5              # via gitpython
-gitpython==3.1.11         # via nbdime
-graphviz==0.15            # via -r .reqs/doc.in
-idna==2.10                # via requests
-imagesize==1.2.0          # via sphinx
-importlib-metadata==3.1.0  # via myst-nb
-ipykernel==5.3.4          # via ipywidgets, jupyter, jupyter-console, notebook, qtconsole
-ipython-genutils==0.2.0   # via nbformat, notebook, qtconsole, traitlets
-ipython==7.19.0           # via ipykernel, ipywidgets, jupyter-console, jupyter-sphinx, myst-nb
-ipywidgets==7.5.1         # via -r .reqs/doc.in, jupyter, jupyter-sphinx, myst-nb
-jedi==0.17.2              # via ipython
-jinja2==2.11.2            # via nbconvert, nbdime, notebook, sphinx
-jsonschema==3.2.0         # via nbformat
-jupyter-cache==0.4.1      # via myst-nb
-jupyter-client==6.1.7     # via ipykernel, jupyter-console, nbclient, notebook, qtconsole
-jupyter-console==6.2.0    # via jupyter
-jupyter-core==4.7.0       # via jupyter-client, nbconvert, nbformat, notebook, qtconsole
-jupyter-sphinx==0.3.2     # via myst-nb
-jupyter==1.0.0            # via -r .reqs/doc.in
-kiwisolver==1.3.1         # via -r .reqs/../requirements.txt, matplotlib
-latexcodec==2.0.1         # via pybtex
-markdown-it-py==0.5.6     # via myst-parser
-markupsafe==1.1.1         # via jinja2
-matplotlib==3.3.3         # via -r .reqs/../requirements.txt
-mistune==0.8.4            # via nbconvert
-myst-nb==0.10.1           # via -r .reqs/doc.in
-myst-parser==0.12.10      # via myst-nb
-nbclient==0.5.1           # via jupyter-cache
-nbconvert==5.6.1          # via jupyter, jupyter-sphinx, myst-nb, notebook
-nbdime==2.1.0             # via jupyter-cache
-nbformat==5.0.8           # via ipywidgets, jupyter-cache, jupyter-sphinx, myst-nb, nbclient, nbconvert, nbdime, notebook
-nest-asyncio==1.4.3       # via nbclient
-notebook==6.1.5           # via jupyter, nbdime, widgetsnbextension
-numpy==1.19.4             # via -r .reqs/../requirements.txt, matplotlib
-oset==0.1.3               # via sphinxcontrib-bibtex
-packaging==20.4           # via bleach, sphinx
-pandocfilters==1.4.3      # via nbconvert
-parso==0.7.1              # via jedi
-pexpect==4.8.0            # via ipython
-pickleshare==0.7.5        # via ipython
-pillow==8.0.1             # via -r .reqs/../requirements.txt, matplotlib
-prometheus-client==0.9.0  # via notebook
-prompt-toolkit==3.0.8     # via ipython, jupyter-console
-ptyprocess==0.6.0         # via pexpect, terminado
-pybtex-docutils==0.2.2    # via sphinxcontrib-bibtex
-pybtex==0.23.0            # via pybtex-docutils, sphinxcontrib-bibtex
-pycparser==2.20           # via cffi
-pydata-sphinx-theme==0.4.1  # via sphinx-book-theme
-pydeps==1.9.11            # via -r .reqs/doc.in
-pygments==2.7.2           # via ipython, jupyter-console, nbconvert, nbdime, qtconsole, sphinx
-pyparsing==2.4.7          # via -r .reqs/../requirements.txt, matplotlib, packaging
-pyrsistent==0.17.3        # via jsonschema
-python-dateutil==2.8.1    # via -r .reqs/../requirements.txt, jupyter-client, matplotlib
-pytz==2020.4              # via babel
-pyyaml==5.3.1             # via myst-nb, myst-parser, pybtex, sphinx-book-theme
-pyzmq==20.0.0             # via jupyter-client, notebook, qtconsole
-qtconsole==5.0.1          # via jupyter
-qtpy==1.9.0               # via qtconsole
-requests==2.25.0          # via nbdime, sphinx
-send2trash==1.5.0         # via notebook
-six==1.15.0               # via -r .reqs/../requirements.txt, argon2-cffi, bleach, cycler, jsonschema, latexcodec, nbdime, packaging, pybtex, pybtex-docutils, python-dateutil
-smmap==3.0.4              # via gitdb
-snowballstemmer==2.0.0    # via sphinx
-soupsieve==2.0.1          # via beautifulsoup4
-sphinx-book-theme==0.0.39  # via -r .reqs/doc.in
-sphinx-copybutton==0.3.1  # via -r .reqs/doc.in
-sphinx-math-dollar==1.2   # via -r .reqs/doc.in
-sphinx-panels==0.5.2      # via -r .reqs/doc.in
-sphinx-thebe==0.0.8       # via -r .reqs/doc.in
-sphinx-togglebutton==0.2.3  # via -r .reqs/doc.in, myst-nb
-sphinx==3.3.1             # via -r .reqs/doc.in, jupyter-sphinx, myst-nb, myst-parser, pydata-sphinx-theme, sphinx-book-theme, sphinx-copybutton, sphinx-math-dollar, sphinx-panels, sphinx-thebe, sphinx-togglebutton, sphinxcontrib-bibtex
-sphinxcontrib-applehelp==1.0.2  # via sphinx
-sphinxcontrib-bibtex==1.0.0  # via -r .reqs/doc.in
-sphinxcontrib-devhelp==1.0.2  # via sphinx
-sphinxcontrib-htmlhelp==1.0.3  # via sphinx
-sphinxcontrib-jsmath==1.0.1  # via sphinx
-sphinxcontrib-qthelp==1.0.3  # via sphinx
-sphinxcontrib-serializinghtml==1.1.4  # via sphinx
-sqlalchemy==1.3.20        # via jupyter-cache
-stdlib-list==0.8.0        # via pydeps
-terminado==0.9.1          # via notebook
-testpath==0.4.4           # via nbconvert
-tornado==6.1              # via ipykernel, jupyter-client, nbdime, notebook, terminado
-traitlets==5.0.5          # via ipykernel, ipython, ipywidgets, jupyter-client, jupyter-core, nbclient, nbconvert, nbformat, notebook, qtconsole
-urllib3==1.26.2           # via requests
-wcwidth==0.2.5            # via prompt-toolkit
-webencodings==0.5.1       # via bleach
-wheel==0.35.1             # via sphinx-togglebutton
-widgetsnbextension==3.5.1  # via ipywidgets
-zipp==3.4.0               # via importlib-metadata
-
-# The following packages are considered to be unsafe in a requirements file:
-# setuptools
diff --git a/.reqs/sty.txt b/.reqs/sty.txt
deleted file mode 100644
index 78140c53..00000000
--- a/.reqs/sty.txt
+++ /dev/null
@@ -1,68 +0,0 @@
-#
-# This file is autogenerated by pip-compile
-# To update, run:
-#
-#    pip-compile .reqs/sty.in
-#
-appdirs==1.4.4            # via black, virtualenv
-astroid==2.4.2            # via pylint
-attrs==20.3.0             # via flake8-bugbear, jsonschema
-black==20.8b1             # via -r .reqs/sty.in
-cfgv==3.2.0               # via pre-commit
-chardet==3.0.4            # via doc8
-click==7.1.2              # via black
-cycler==0.10.0            # via -r .reqs/../requirements.txt, matplotlib
-distlib==0.3.1            # via virtualenv
-doc8==0.8.1               # via -r .reqs/sty.in
-docutils==0.16            # via doc8, restructuredtext-lint, rstcheck
-filelock==3.0.12          # via virtualenv
-flake8-blind-except==0.1.1  # via -r .reqs/sty.in
-flake8-bugbear==20.11.1   # via -r .reqs/sty.in
-flake8-builtins==1.5.3    # via -r .reqs/sty.in
-flake8-polyfill==1.0.2    # via pep8-naming
-flake8-rst-docstrings==0.0.14  # via -r .reqs/sty.in
-flake8==3.8.4             # via -r .reqs/sty.in, flake8-bugbear, flake8-builtins, flake8-polyfill, flake8-rst-docstrings
-identify==1.5.10          # via pre-commit
-ipython-genutils==0.2.0   # via nbformat, traitlets
-isort==5.6.4              # via -r .reqs/sty.in, pylint
-jsonschema==3.2.0         # via nbformat
-jupyter-core==4.7.0       # via nbformat
-kiwisolver==1.3.1         # via -r .reqs/../requirements.txt, matplotlib
-lazy-object-proxy==1.4.3  # via astroid
-matplotlib==3.3.3         # via -r .reqs/../requirements.txt
-mccabe==0.6.1             # via flake8, pylint
-mypy-extensions==0.4.3    # via black, mypy
-mypy==0.790               # via -r .reqs/sty.in
-nbformat==5.0.8           # via nbstripout
-nbstripout==0.3.9         # via -r .reqs/sty.in
-nodeenv==1.5.0            # via pre-commit
-numpy==1.19.4             # via -r .reqs/../requirements.txt, matplotlib
-pathspec==0.8.1           # via black
-pbr==5.5.1                # via stevedore
-pep8-naming==0.11.1       # via -r .reqs/sty.in
-pillow==8.0.1             # via -r .reqs/../requirements.txt, matplotlib
-pre-commit==2.9.0         # via -r .reqs/sty.in
-pycodestyle==2.6.0        # via flake8
-pydocstyle==5.1.1         # via -r .reqs/sty.in
-pyflakes==2.2.0           # via flake8
-pygments==2.7.2           # via doc8
-pylint==2.6.0             # via -r .reqs/sty.in
-pyparsing==2.4.7          # via -r .reqs/../requirements.txt, matplotlib
-pyrsistent==0.17.3        # via jsonschema
-python-dateutil==2.8.1    # via -r .reqs/../requirements.txt, matplotlib
-pyyaml==5.3.1             # via pre-commit
-regex==2020.11.13         # via black
-restructuredtext-lint==1.3.2  # via doc8, flake8-rst-docstrings
-rstcheck==3.3.1           # via -r .reqs/sty.in
-six==1.15.0               # via -r .reqs/../requirements.txt, astroid, cycler, doc8, jsonschema, python-dateutil, virtualenv
-snowballstemmer==2.0.0    # via pydocstyle
-stevedore==3.2.2          # via doc8
-toml==0.10.2              # via black, pre-commit, pylint
-traitlets==5.0.5          # via jupyter-core, nbformat
-typed-ast==1.4.1          # via black, mypy
-typing-extensions==3.7.4.3  # via black, mypy
-virtualenv==20.2.1        # via pre-commit
-wrapt==1.12.1             # via astroid
-
-# The following packages are considered to be unsafe in a requirements file:
-# setuptools
diff --git a/.vscode/settings.json b/.vscode/settings.json
index ec70ee39..09fef50a 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -37,6 +37,12 @@
   "files.associations": {
     "*.inc": "restructuredtext"
   },
+  "files.watcherExclude": {
+    "**/*_cache/**": true,
+    "**/.eggs/**": true,
+    "**/.git/**": true,
+    "**/.tox/**": true
+  },
   "git.rebaseWhenSync": true,
   "githubPullRequests.telemetry.enabled": false,
   "gitlens.advanced.telemetry.enabled": false,
@@ -62,8 +68,8 @@
   "rewrap.wrappingColumn": 79,
   "search.exclude": {
     "**/tests/**/__init__.py": true,
-    ".reqs/*.txt": true,
     "docs/tox.ini": true,
+    "reqs/3.*/*.txt": true,
     "tests/tox.ini": true
   },
   "telemetry.enableCrashReporter": false,
diff --git a/cspell.json b/cspell.json
index 7f3f165d..9c04c465 100644
--- a/cspell.json
+++ b/cspell.json
@@ -2,8 +2,7 @@
     "version": "0.1",
     "enableFiletypes": [
         "git-commit",
-        "jupyter",
-        "xml"
+        "jupyter"
     ],
     "flagWords": [
         "analyse",
@@ -28,8 +27,6 @@
         ".pre-commit-config.yaml",
         ".pylintrc",
         ".readthedocs.yml",
-        ".reqs/*.in",
-        ".reqs/*.txt",
         ".vscode/*",
         ".vscode/.gitignore",
         "Makefile",
@@ -39,6 +36,8 @@
         "docs/conf.py",
         "pyproject.toml",
         "pyrightconfig.json",
+        "reqs/**/*.in",
+        "reqs/**/*.txt",
         "requirements*.txt",
         "setup.cfg",
         "setup.py",
@@ -119,6 +118,7 @@
         "pytest",
         "rarita",
         "rebased",
+        "reqs",
         "rightarrow",
         "rtfd",
         "scikit",
diff --git a/docs/develop.md b/docs/develop.md
index fa78973b..a64cdc08 100644
--- a/docs/develop.md
+++ b/docs/develop.md
@@ -192,7 +192,7 @@ Where possible, we define and enforce our coding conventions through automated
 tools, instead of describing them in documentation. These tools perform their
 checks when you commit files locally (see {ref}`develop:Pre-commit`), when
 {ref}`running tox <develop:tox>`, and when you make a
-{ref}`pull request <develop:Git and GitHub>`.
+{ref}`pull request <develop:Collaboration>`.
 
 The tools are configured through files such as
 [`pyproject.toml`](https://github.com/ComPWA/PWA-pages/blob/master/pyproject.toml),
@@ -203,7 +203,7 @@ workflow files under
 run into persistent linting errors, this may mean we need to further specify
 our conventions. In that case, it's best to
 {ref}`create an issue <develop:Issue management>` or a
-{ref}`pull request <develop:Git and GitHub>` and propose a policy change that
+{ref}`pull request <develop:Collaboration>` and propose a policy change that
 can be formulated through those config files.
 
 ### Pre-commit
@@ -270,7 +270,7 @@ environments install
 
 ### GitHub Actions
 
-All {ref}`style checks <develop:Automated style checks>`, testing of the
+All {ref}`style checks <develop:Style checks>`, testing of the
 {ref}`documentation and links <develop:Documentation>`, and
 {ref}`unit tests <develop:Testing>` are performed upon each pull request
 through [GitHub Actions](https://docs.github.com/en/actions) (see status
@@ -472,16 +472,16 @@ or [Markdown](https://www.markdownguide.org). In addition, it's easy to write
 
 ````{margin}
 ```{tip}
-Sometimes it happens that your Jupyter installation does not recognize
-your {ref}`virtual environment <install:Step 2: Create a virtual environment>`.
-In that case, have a look at
+Sometimes it happens that your Jupyter installation does not recognize your
+{ref}`virtual environment <develop:Virtual environment>`. In that case, have a
+look at
 [these instructions](https://ipython.readthedocs.io/en/stable/install/kernel_install.html#kernels-for-different-environments)
 ```
 ````
 
 The [docs](https://github.com/ComPWA/PWA-pages/tree/master/docs) folder
 contains a few Jupyter notebooks. These notebooks are run and tested whenever
-you make a {ref}`pull request <develop:Git and GitHub>`. If you want to improve
+you make a {ref}`pull request <develop:Collaboration>`. If you want to improve
 those notebooks, we recommend working with
 [Jupyter Lab](https://jupyterlab.readthedocs.io/en/stable), which is
 {ref}`installed with the dev requirements <develop:Additional dependencies>`.
@@ -560,9 +560,9 @@ The documentation of the `stable` branch is also the default view
 #### `master` branch
 
 Represents the upcoming release of the package. This branch is not guaranteed
-to be stable, but has high {ref}`CI standards <develop:Continuous Integration>`
-and can only be updated through reviewed pull requests. The documentation of
-the `master` branch can be found on RTD under "latest", see e.g.
+to be stable, but has high {ref}`CI standards <develop:GitHub Actions>` and can
+only be updated through reviewed pull requests. The documentation of the
+`master` branch can be found on RTD under "latest", see e.g.
 [expertsystem.rtfd.io/en/latest](https://expertsystem.rtfd.io/en/latest).
 
 #### Epic branches
diff --git a/environment.yml b/environment.yml
index 1b9f166c..e3ef9483 100644
--- a/environment.yml
+++ b/environment.yml
@@ -2,9 +2,9 @@ name: pwa-pages
 channels:
   - defaults
 dependencies:
-  - python>=3.6,<3.9
+  - python==3.8.*
   - pip
   - graphviz # for binder
   - pip:
-      - -r requirements-dev.txt
+      - -r reqs/3.8/requirements-dev.txt
       - -e .
diff --git a/labels.toml b/labels.toml
index 915753e5..b52063c9 100644
--- a/labels.toml
+++ b/labels.toml
@@ -8,6 +8,11 @@ color = "3E4B9E"
 name = "Epic"
 description = ""
 
+["⚠️ Interface"]
+color = "BFDADC"
+name = "⚠️ Interface"
+description = "Changes to the interface"
+
 ["⚪ Duplicate"]
 color = "cfd3d7"
 name = "⚪ Duplicate"
@@ -23,10 +28,10 @@ color = "88506B"
 name = "❔ Question"
 description = "Discuss this matter in the team"
 
-["💡 Enhancement"]
+["💡 Feature"]
 color = "c2e0c6"
-name = "💡 Enhancement"
-description = "New feature or improvement of existing code"
+name = "💡 Feature"
+description = "New feature added to the package"
 
 ["💫 Good first issue"]
 color = "F4EAEF"
@@ -56,7 +61,7 @@ description = "Improvements or additions to documentation"
 ["🔨 Maintenance"]
 color = "FFCD8F"
 name = "🔨 Maintenance"
-description = "Refactoring or redesign"
+description = "Refactoring that doesn't affect the interface"
 
 ["🖱️ DX"]
 color = "fef2c0"
diff --git a/reqs/.gitignore b/reqs/.gitignore
new file mode 100644
index 00000000..8d0647e4
--- /dev/null
+++ b/reqs/.gitignore
@@ -0,0 +1,2 @@
+requirements.in
+*/requirements*.in
diff --git a/reqs/3.6/requirements-dev.txt b/reqs/3.6/requirements-dev.txt
new file mode 100644
index 00000000..a32a25cd
--- /dev/null
+++ b/reqs/3.6/requirements-dev.txt
@@ -0,0 +1,177 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.6/requirements-dev.txt reqs/requirements-dev.in reqs/requirements-doc.in reqs/requirements-sty.in reqs/requirements.in
+#
+alabaster==0.7.12
+anyio==2.0.2
+appdirs==1.4.4
+argon2-cffi==20.1.0
+astroid==2.4.2
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+black==20.8b1
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+contextvars==2.4
+cycler==0.10.0
+dataclasses==0.8
+decorator==4.4.2
+defusedxml==0.6.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+entrypoints==0.3
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+identify==1.5.12
+idna==2.10
+imagesize==1.2.0
+immutables==0.14
+importlib-metadata==3.4.0
+importlib-resources==3.0.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.16.1
+ipywidgets==7.6.3
+isort==5.7.0
+jedi==0.18.0
+jinja2==2.11.2
+json5==0.9.5
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-server==1.2.2
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-code-formatter==1.4.2
+jupyterlab-server==2.1.2
+jupyterlab-widgets==1.0.0
+jupyterlab==3.0.5
+kiwisolver==1.3.1
+labels==20.1.0
+latexcodec==2.0.1
+lazy-object-proxy==1.4.3
+livereload==2.6.3
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mccabe==0.6.1
+mistune==0.8.4
+mypy-extensions==0.4.3
+mypy==0.790
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclassic==0.2.6
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nbstripout==0.3.9
+nest-asyncio==1.4.3
+nodeenv==1.5.0
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+pip-tools==5.5.0
+pluggy==0.13.1
+pre-commit==2.9.3
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+py==1.10.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycodestyle==2.6.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytoml==0.1.21
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+regex==2020.11.13
+requests==2.25.1
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+sniffio==1.2.0
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-autobuild==2020.9.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+stevedore==3.3.0
+terminado==0.9.2
+testpath==0.4.4
+toml==0.10.2
+tornado==6.1
+tox==3.21.1
+traitlets==4.3.3
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+virtualenv==20.3.1
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools
diff --git a/reqs/3.6/requirements-doc.txt b/reqs/3.6/requirements-doc.txt
new file mode 100644
index 00000000..3fb85f9d
--- /dev/null
+++ b/reqs/3.6/requirements-doc.txt
@@ -0,0 +1,120 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.6/requirements-doc.txt reqs/3.6/requirements-doc.in
+#
+alabaster==0.7.12
+argon2-cffi==20.1.0
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+docutils==0.16
+entrypoints==0.3
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+importlib-resources==3.0.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.16.1
+ipywidgets==7.6.3
+jedi==0.18.0
+jinja2==2.11.2
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-widgets==1.0.0
+kiwisolver==1.3.1
+latexcodec==2.0.1
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mistune==0.8.4
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nest-asyncio==1.4.3
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pygments==2.7.4
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+requests==2.25.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+terminado==0.9.2
+testpath==0.4.4
+tornado==6.1
+traitlets==4.3.3
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.6/requirements-sty.txt b/reqs/3.6/requirements-sty.txt
new file mode 100644
index 00000000..6fe574df
--- /dev/null
+++ b/reqs/3.6/requirements-sty.txt
@@ -0,0 +1,73 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.6/requirements-sty.txt reqs/3.6/requirements-sty.in
+#
+appdirs==1.4.4
+astroid==2.4.2
+attrs==20.3.0
+black==20.8b1
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+cycler==0.10.0
+dataclasses==0.8
+decorator==4.4.2
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+identify==1.5.12
+importlib-metadata==3.4.0
+importlib-resources==3.0.0
+ipython-genutils==0.2.0
+isort==5.7.0
+jsonschema==3.2.0
+jupyter-core==4.7.0
+kiwisolver==1.3.1
+lazy-object-proxy==1.4.3
+matplotlib==3.3.3
+mccabe==0.6.1
+mypy-extensions==0.4.3
+mypy==0.790
+nbformat==5.1.2
+nbstripout==0.3.9
+nodeenv==1.5.0
+numpy==1.19.5
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pillow==8.1.0
+pre-commit==2.9.3
+pycodestyle==2.6.0
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pyyaml==5.3.1
+regex==2020.11.13
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+six==1.15.0
+snowballstemmer==2.0.0
+stevedore==3.3.0
+toml==0.10.2
+traitlets==4.3.3
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+virtualenv==20.3.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.6/requirements.txt b/reqs/3.6/requirements.txt
new file mode 100644
index 00000000..cfca8b19
--- /dev/null
+++ b/reqs/3.6/requirements.txt
@@ -0,0 +1,14 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.6/requirements.txt reqs/3.6/requirements.in
+#
+cycler==0.10.0
+kiwisolver==1.3.1
+matplotlib==3.3.3
+numpy==1.19.5
+pillow==8.1.0
+pyparsing==2.4.7
+python-dateutil==2.8.1
+six==1.15.0
diff --git a/reqs/3.7/requirements-dev.txt b/reqs/3.7/requirements-dev.txt
new file mode 100644
index 00000000..eed5ce90
--- /dev/null
+++ b/reqs/3.7/requirements-dev.txt
@@ -0,0 +1,173 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.7/requirements-dev.txt reqs/requirements-dev.in reqs/requirements-doc.in reqs/requirements-sty.in reqs/requirements.in
+#
+alabaster==0.7.12
+anyio==2.0.2
+appdirs==1.4.4
+argon2-cffi==20.1.0
+astroid==2.4.2
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+black==20.8b1
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+entrypoints==0.3
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+identify==1.5.12
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+isort==5.7.0
+jedi==0.18.0
+jinja2==2.11.2
+json5==0.9.5
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-server==1.2.2
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-code-formatter==1.4.2
+jupyterlab-server==2.1.2
+jupyterlab-widgets==1.0.0
+jupyterlab==3.0.5
+kiwisolver==1.3.1
+labels==20.1.0
+latexcodec==2.0.1
+lazy-object-proxy==1.4.3
+livereload==2.6.3
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mccabe==0.6.1
+mistune==0.8.4
+mypy-extensions==0.4.3
+mypy==0.790
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclassic==0.2.6
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nbstripout==0.3.9
+nest-asyncio==1.4.3
+nodeenv==1.5.0
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+pip-tools==5.5.0
+pluggy==0.13.1
+pre-commit==2.9.3
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+py==1.10.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycodestyle==2.6.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytoml==0.1.21
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+regex==2020.11.13
+requests==2.25.1
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+sniffio==1.2.0
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-autobuild==2020.9.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+stevedore==3.3.0
+terminado==0.9.2
+testpath==0.4.4
+toml==0.10.2
+tornado==6.1
+tox==3.21.1
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+virtualenv==20.3.1
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools
diff --git a/reqs/3.7/requirements-doc.txt b/reqs/3.7/requirements-doc.txt
new file mode 100644
index 00000000..0e23fa75
--- /dev/null
+++ b/reqs/3.7/requirements-doc.txt
@@ -0,0 +1,119 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.7/requirements-doc.txt reqs/3.7/requirements-doc.in
+#
+alabaster==0.7.12
+argon2-cffi==20.1.0
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+docutils==0.16
+entrypoints==0.3
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+jedi==0.18.0
+jinja2==2.11.2
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-widgets==1.0.0
+kiwisolver==1.3.1
+latexcodec==2.0.1
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mistune==0.8.4
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nest-asyncio==1.4.3
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pygments==2.7.4
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+requests==2.25.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+terminado==0.9.2
+testpath==0.4.4
+tornado==6.1
+traitlets==5.0.5
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.7/requirements-sty.txt b/reqs/3.7/requirements-sty.txt
new file mode 100644
index 00000000..bceb2f58
--- /dev/null
+++ b/reqs/3.7/requirements-sty.txt
@@ -0,0 +1,70 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.7/requirements-sty.txt reqs/3.7/requirements-sty.in
+#
+appdirs==1.4.4
+astroid==2.4.2
+attrs==20.3.0
+black==20.8b1
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+cycler==0.10.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+identify==1.5.12
+importlib-metadata==3.4.0
+ipython-genutils==0.2.0
+isort==5.7.0
+jsonschema==3.2.0
+jupyter-core==4.7.0
+kiwisolver==1.3.1
+lazy-object-proxy==1.4.3
+matplotlib==3.3.3
+mccabe==0.6.1
+mypy-extensions==0.4.3
+mypy==0.790
+nbformat==5.1.2
+nbstripout==0.3.9
+nodeenv==1.5.0
+numpy==1.19.5
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pillow==8.1.0
+pre-commit==2.9.3
+pycodestyle==2.6.0
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pyyaml==5.3.1
+regex==2020.11.13
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+six==1.15.0
+snowballstemmer==2.0.0
+stevedore==3.3.0
+toml==0.10.2
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+virtualenv==20.3.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.7/requirements.txt b/reqs/3.7/requirements.txt
new file mode 100644
index 00000000..f8f73e13
--- /dev/null
+++ b/reqs/3.7/requirements.txt
@@ -0,0 +1,14 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.7/requirements.txt reqs/3.7/requirements.in
+#
+cycler==0.10.0
+kiwisolver==1.3.1
+matplotlib==3.3.3
+numpy==1.19.5
+pillow==8.1.0
+pyparsing==2.4.7
+python-dateutil==2.8.1
+six==1.15.0
diff --git a/reqs/3.8/requirements-dev.txt b/reqs/3.8/requirements-dev.txt
new file mode 100644
index 00000000..85ce8d7e
--- /dev/null
+++ b/reqs/3.8/requirements-dev.txt
@@ -0,0 +1,173 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.8/requirements-dev.txt reqs/requirements-dev.in reqs/requirements-doc.in reqs/requirements-sty.in reqs/requirements.in
+#
+alabaster==0.7.12
+anyio==2.0.2
+appdirs==1.4.4
+argon2-cffi==20.1.0
+astroid==2.4.2
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+black==20.8b1
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+entrypoints==0.3
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+identify==1.5.12
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+isort==5.7.0
+jedi==0.18.0
+jinja2==2.11.2
+json5==0.9.5
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-server==1.2.2
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-code-formatter==1.4.2
+jupyterlab-server==2.1.2
+jupyterlab-widgets==1.0.0
+jupyterlab==3.0.5
+kiwisolver==1.3.1
+labels==20.1.0
+latexcodec==2.0.1
+lazy-object-proxy==1.4.3
+livereload==2.6.3
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mccabe==0.6.1
+mistune==0.8.4
+mypy-extensions==0.4.3
+mypy==0.790
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclassic==0.2.6
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nbstripout==0.3.9
+nest-asyncio==1.4.3
+nodeenv==1.5.0
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+pip-tools==5.5.0
+pluggy==0.13.1
+pre-commit==2.9.3
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+py==1.10.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycodestyle==2.6.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytoml==0.1.21
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+regex==2020.11.13
+requests==2.25.1
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+sniffio==1.2.0
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-autobuild==2020.9.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+stevedore==3.3.0
+terminado==0.9.2
+testpath==0.4.4
+toml==0.10.2
+tornado==6.1
+tox==3.21.1
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+virtualenv==20.3.1
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools
diff --git a/reqs/3.8/requirements-doc.txt b/reqs/3.8/requirements-doc.txt
new file mode 100644
index 00000000..4848faa5
--- /dev/null
+++ b/reqs/3.8/requirements-doc.txt
@@ -0,0 +1,118 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.8/requirements-doc.txt reqs/3.8/requirements-doc.in
+#
+alabaster==0.7.12
+argon2-cffi==20.1.0
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+docutils==0.16
+entrypoints==0.3
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+jedi==0.18.0
+jinja2==2.11.2
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-widgets==1.0.0
+kiwisolver==1.3.1
+latexcodec==2.0.1
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mistune==0.8.4
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nest-asyncio==1.4.3
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pygments==2.7.4
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+requests==2.25.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+terminado==0.9.2
+testpath==0.4.4
+tornado==6.1
+traitlets==5.0.5
+urllib3==1.26.2
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.8/requirements-sty.txt b/reqs/3.8/requirements-sty.txt
new file mode 100644
index 00000000..c087bb7c
--- /dev/null
+++ b/reqs/3.8/requirements-sty.txt
@@ -0,0 +1,68 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.8/requirements-sty.txt reqs/3.8/requirements-sty.in
+#
+appdirs==1.4.4
+astroid==2.4.2
+attrs==20.3.0
+black==20.8b1
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+cycler==0.10.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+identify==1.5.12
+ipython-genutils==0.2.0
+isort==5.7.0
+jsonschema==3.2.0
+jupyter-core==4.7.0
+kiwisolver==1.3.1
+lazy-object-proxy==1.4.3
+matplotlib==3.3.3
+mccabe==0.6.1
+mypy-extensions==0.4.3
+mypy==0.790
+nbformat==5.1.2
+nbstripout==0.3.9
+nodeenv==1.5.0
+numpy==1.19.5
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pillow==8.1.0
+pre-commit==2.9.3
+pycodestyle==2.6.0
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pyyaml==5.3.1
+regex==2020.11.13
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+six==1.15.0
+snowballstemmer==2.0.0
+stevedore==3.3.0
+toml==0.10.2
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+virtualenv==20.3.1
+wrapt==1.12.1
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.8/requirements.txt b/reqs/3.8/requirements.txt
new file mode 100644
index 00000000..36297251
--- /dev/null
+++ b/reqs/3.8/requirements.txt
@@ -0,0 +1,14 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.8/requirements.txt reqs/3.8/requirements.in
+#
+cycler==0.10.0
+kiwisolver==1.3.1
+matplotlib==3.3.3
+numpy==1.19.5
+pillow==8.1.0
+pyparsing==2.4.7
+python-dateutil==2.8.1
+six==1.15.0
diff --git a/reqs/3.9/requirements-dev.txt b/reqs/3.9/requirements-dev.txt
new file mode 100644
index 00000000..ae7acb83
--- /dev/null
+++ b/reqs/3.9/requirements-dev.txt
@@ -0,0 +1,173 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.9/requirements-dev.txt reqs/requirements-dev.in reqs/requirements-doc.in reqs/requirements-sty.in reqs/requirements.in
+#
+alabaster==0.7.12
+anyio==2.0.2
+appdirs==1.4.4
+argon2-cffi==20.1.0
+astroid==2.4.2
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+black==20.8b1
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+entrypoints==0.3
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+identify==1.5.12
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+isort==5.7.0
+jedi==0.18.0
+jinja2==2.11.2
+json5==0.9.5
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-server==1.2.2
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-code-formatter==1.4.2
+jupyterlab-server==2.1.2
+jupyterlab-widgets==1.0.0
+jupyterlab==3.0.5
+kiwisolver==1.3.1
+labels==20.1.0
+latexcodec==2.0.1
+lazy-object-proxy==1.4.3
+livereload==2.6.3
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mccabe==0.6.1
+mistune==0.8.4
+mypy-extensions==0.4.3
+mypy==0.790
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclassic==0.2.6
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nbstripout==0.3.9
+nest-asyncio==1.4.3
+nodeenv==1.5.0
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+pip-tools==5.5.0
+pluggy==0.13.1
+pre-commit==2.9.3
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+py==1.10.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycodestyle==2.6.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytoml==0.1.21
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+regex==2020.11.13
+requests==2.25.1
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+sniffio==1.2.0
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-autobuild==2020.9.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+stevedore==3.3.0
+terminado==0.9.2
+testpath==0.4.4
+toml==0.10.2
+tornado==6.1
+tox==3.21.1
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+urllib3==1.26.2
+virtualenv==20.3.1
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+wrapt==1.12.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools
diff --git a/reqs/3.9/requirements-doc.txt b/reqs/3.9/requirements-doc.txt
new file mode 100644
index 00000000..5466bf51
--- /dev/null
+++ b/reqs/3.9/requirements-doc.txt
@@ -0,0 +1,118 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.9/requirements-doc.txt reqs/3.9/requirements-doc.in
+#
+alabaster==0.7.12
+argon2-cffi==20.1.0
+async-generator==1.10
+attrs==20.3.0
+babel==2.9.0
+backcall==0.2.0
+beautifulsoup4==4.9.3
+bleach==3.2.1
+certifi==2020.12.5
+cffi==1.14.4
+chardet==4.0.0
+click==7.1.2
+colorama==0.4.4
+cycler==0.10.0
+decorator==4.4.2
+defusedxml==0.6.0
+docutils==0.16
+entrypoints==0.3
+gitdb==4.0.5
+gitpython==3.1.12
+graphviz==0.16
+idna==2.10
+imagesize==1.2.0
+importlib-metadata==3.4.0
+ipykernel==5.4.3
+ipython-genutils==0.2.0
+ipython==7.19.0
+ipywidgets==7.6.3
+jedi==0.18.0
+jinja2==2.11.2
+jsonschema==3.2.0
+jupyter-cache==0.4.1
+jupyter-client==6.1.11
+jupyter-console==6.2.0
+jupyter-core==4.7.0
+jupyter-sphinx==0.3.1
+jupyter==1.0.0
+jupyterlab-widgets==1.0.0
+kiwisolver==1.3.1
+latexcodec==2.0.1
+markdown-it-py==0.5.8
+markupsafe==1.1.1
+matplotlib==3.3.3
+mistune==0.8.4
+myst-nb==0.10.2
+myst-parser==0.12.10
+nbclient==0.5.1
+nbconvert==5.6.1
+nbdime==2.1.0
+nbformat==5.1.2
+nest-asyncio==1.4.3
+notebook==6.2.0
+numpy==1.19.5
+oset==0.1.3
+packaging==20.8
+pandocfilters==1.4.3
+parso==0.8.1
+pexpect==4.8.0
+pickleshare==0.7.5
+pillow==8.1.0
+prometheus-client==0.9.0
+prompt-toolkit==3.0.10
+ptyprocess==0.7.0
+pybtex-docutils==1.0.0
+pybtex==0.23.0
+pycparser==2.20
+pydata-sphinx-theme==0.4.1
+pydeps==1.9.13
+pygments==2.7.4
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytz==2020.5
+pyyaml==5.3.1
+pyzmq==21.0.1
+qtconsole==5.0.1
+qtpy==1.9.0
+requests==2.25.1
+send2trash==1.5.0
+six==1.15.0
+smmap==3.0.4
+snowballstemmer==2.0.0
+soupsieve==2.1
+sphinx-book-theme==0.0.39
+sphinx-copybutton==0.3.1
+sphinx-math-dollar==1.2
+sphinx-panels==0.5.2
+sphinx-thebe==0.0.8
+sphinx-togglebutton==0.2.3
+sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-bibtex==1.0.0
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+sqlalchemy==1.3.22
+stdlib-list==0.8.0
+terminado==0.9.2
+testpath==0.4.4
+tornado==6.1
+traitlets==5.0.5
+urllib3==1.26.2
+wcwidth==0.2.5
+webencodings==0.5.1
+wheel==0.36.2
+widgetsnbextension==3.5.1
+zipp==3.4.0
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.9/requirements-sty.txt b/reqs/3.9/requirements-sty.txt
new file mode 100644
index 00000000..183c397d
--- /dev/null
+++ b/reqs/3.9/requirements-sty.txt
@@ -0,0 +1,68 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.9/requirements-sty.txt reqs/3.9/requirements-sty.in
+#
+appdirs==1.4.4
+astroid==2.4.2
+attrs==20.3.0
+black==20.8b1
+cfgv==3.2.0
+chardet==4.0.0
+click==7.1.2
+cycler==0.10.0
+distlib==0.3.1
+doc8==0.8.1
+docutils==0.16
+filelock==3.0.12
+flake8-blind-except==0.2.0
+flake8-bugbear==20.11.1
+flake8-builtins==1.5.3
+flake8-polyfill==1.0.2
+flake8-rst-docstrings==0.0.14
+flake8==3.8.4
+identify==1.5.12
+ipython-genutils==0.2.0
+isort==5.7.0
+jsonschema==3.2.0
+jupyter-core==4.7.0
+kiwisolver==1.3.1
+lazy-object-proxy==1.4.3
+matplotlib==3.3.3
+mccabe==0.6.1
+mypy-extensions==0.4.3
+mypy==0.790
+nbformat==5.1.2
+nbstripout==0.3.9
+nodeenv==1.5.0
+numpy==1.19.5
+pathspec==0.8.1
+pbr==5.5.1
+pep8-naming==0.11.1
+pillow==8.1.0
+pre-commit==2.9.3
+pycodestyle==2.6.0
+pydocstyle==5.1.1
+pyflakes==2.2.0
+pygments==2.7.4
+pylint==2.6.0
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pyyaml==5.3.1
+regex==2020.11.13
+restructuredtext-lint==1.3.2
+rstcheck==3.3.1
+six==1.15.0
+snowballstemmer==2.0.0
+stevedore==3.3.0
+toml==0.10.2
+traitlets==5.0.5
+typed-ast==1.4.2
+typing-extensions==3.7.4.3
+virtualenv==20.3.1
+wrapt==1.12.1
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools
diff --git a/reqs/3.9/requirements.txt b/reqs/3.9/requirements.txt
new file mode 100644
index 00000000..a9294b46
--- /dev/null
+++ b/reqs/3.9/requirements.txt
@@ -0,0 +1,14 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --no-annotate --output-file=reqs/3.9/requirements.txt reqs/3.9/requirements.in
+#
+cycler==0.10.0
+kiwisolver==1.3.1
+matplotlib==3.3.3
+numpy==1.19.5
+pillow==8.1.0
+pyparsing==2.4.7
+python-dateutil==2.8.1
+six==1.15.0
diff --git a/reqs/extract_install_requires.py b/reqs/extract_install_requires.py
new file mode 100644
index 00000000..39484f39
--- /dev/null
+++ b/reqs/extract_install_requires.py
@@ -0,0 +1,18 @@
+"""Extract :code:`install_requires` section to :file:`requirements.in`."""
+
+import configparser
+from os.path import dirname, realpath
+
+
+def main() -> None:
+    script_dir = dirname(realpath(__file__))
+    cfg = configparser.ConfigParser()
+    cfg.read(f"{script_dir}/../setup.cfg")
+    install_requires = cfg.get("options", "install_requires", raw=False)
+    install_requires = install_requires[1:]  # remove first line (empty)
+    with open(f"{script_dir}/requirements.in", "w") as stream:
+        stream.write(install_requires)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/reqs/requirements-dev.in b/reqs/requirements-dev.in
new file mode 100644
index 00000000..948a5d4f
--- /dev/null
+++ b/reqs/requirements-dev.in
@@ -0,0 +1,11 @@
+-r requirements.in
+-r requirements-doc.in
+-r requirements-sty.in
+
+# Additional developer tools
+jupyterlab
+jupyterlab-code-formatter
+labels
+pip-tools
+sphinx-autobuild
+tox >= 1.9  # for skip_install, use_develop
diff --git a/.reqs/doc.in b/reqs/requirements-doc.in
similarity index 68%
rename from .reqs/doc.in
rename to reqs/requirements-doc.in
index 3108d339..02673b08 100644
--- a/.reqs/doc.in
+++ b/reqs/requirements-doc.in
@@ -1,10 +1,10 @@
--r ../requirements.txt
+-r requirements.in
 
 # Requirements to build documentation
 graphviz
 ipywidgets
 jupyter
-myst-nb
+myst-nb < 0.11  # myst_admonition_enable
 pydeps
 Sphinx >= 3
 sphinx-book-theme
@@ -13,4 +13,4 @@ sphinx-math-dollar
 sphinx-panels
 sphinx-thebe
 sphinx-togglebutton
-sphinxcontrib-bibtex
+sphinxcontrib-bibtex < 2
diff --git a/.reqs/sty.in b/reqs/requirements-sty.in
similarity index 85%
rename from .reqs/sty.in
rename to reqs/requirements-sty.in
index 53ed3f8b..7cc691fa 100644
--- a/.reqs/sty.in
+++ b/reqs/requirements-sty.in
@@ -1,4 +1,4 @@
--r ../requirements.txt
+-r requirements.in
 
 pre-commit >= 1.4.0
 
@@ -13,7 +13,7 @@ flake8-blind-except
 flake8-bugbear
 flake8-builtins
 flake8-rst-docstrings
-mypy
+mypy >= 0.570  # attrs support
 pep8-naming
 pydocstyle
 pylint
diff --git a/reqs/upgrade.sh b/reqs/upgrade.sh
new file mode 100644
index 00000000..65a81c46
--- /dev/null
+++ b/reqs/upgrade.sh
@@ -0,0 +1,28 @@
+# https://github.com/jazzband/pip-tools/issues/625
+
+PYTHON_VERSION=$(python -c 'import sys; print(".".join(map(str, sys.version_info[:2])))')
+
+if [[ -z "$PYTHON_VERSION" ]]; then
+    echo -e "\e[31;1mERROR: environment variable PYTHON_VERSION needs to be defined!\e[0m"
+    exit 1
+fi
+
+mkdir -p reqs/$PYTHON_VERSION &&
+    python reqs/extract_install_requires.py &&
+    cp reqs/requirements*.in reqs/$PYTHON_VERSION/ &&
+    rm reqs/$PYTHON_VERSION/requirements-dev.in &&
+    pip-compile --upgrade \
+        --no-annotate \
+        reqs/requirements*.in \
+        -o reqs/$PYTHON_VERSION/requirements-dev.txt &&
+    for in_file in $(ls reqs/$PYTHON_VERSION/requirements*.in); do
+        echo -e "-c requirements-dev.txt\n$(cat ${in_file})" >${in_file}
+        out_file="${in_file/.in/.txt}"
+        pip-compile "${in_file}" -o "${out_file}" --no-annotate
+        # https://github.com/jazzband/pip-tools/issues/431#issuecomment-277300235
+        sed -i -e 's/typing_extensions/typing-extensions/g' "${out_file}"
+    done &&
+    pip-sync reqs/$PYTHON_VERSION/requirements*.txt &&
+    exit 0
+
+exit 1 # if failure
diff --git a/requirements-dev.txt b/requirements-dev.txt
deleted file mode 100644
index ac10a22e..00000000
--- a/requirements-dev.txt
+++ /dev/null
@@ -1,166 +0,0 @@
-#
-# This file is autogenerated by pip-compile
-# To update, run:
-#
-#    pip-compile --output-file=requirements-dev.txt .reqs/dev.in
-#
-alabaster==0.7.12         # via -r .reqs/doc.txt, sphinx
-appdirs==1.4.4            # via -r .reqs/sty.txt, black, virtualenv
-argon2-cffi==20.1.0       # via -r .reqs/doc.txt, notebook
-astroid==2.4.2            # via -r .reqs/sty.txt, pylint
-async-generator==1.10     # via -r .reqs/doc.txt, nbclient
-attrs==20.3.0             # via -r .reqs/doc.txt, -r .reqs/sty.txt, flake8-bugbear, jsonschema, jupyter-cache, labels, markdown-it-py
-babel==2.9.0              # via -r .reqs/doc.txt, sphinx
-backcall==0.2.0           # via -r .reqs/doc.txt, ipython
-beautifulsoup4==4.9.3     # via -r .reqs/doc.txt, sphinx-book-theme
-black==20.8b1             # via -r .reqs/sty.txt
-bleach==3.2.1             # via -r .reqs/doc.txt, nbconvert
-certifi==2020.11.8        # via -r .reqs/doc.txt, requests
-cffi==1.14.4              # via -r .reqs/doc.txt, argon2-cffi
-cfgv==3.2.0               # via -r .reqs/sty.txt, pre-commit
-chardet==3.0.4            # via -r .reqs/doc.txt, -r .reqs/sty.txt, doc8, requests
-click==7.1.2              # via -r .reqs/doc.txt, -r .reqs/sty.txt, black, labels, pip-tools, sphinx-book-theme
-colorama==0.4.4           # via -r .reqs/doc.txt, nbdime
-cycler==0.10.0            # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, matplotlib
-decorator==4.4.2          # via -r .reqs/doc.txt, ipython
-defusedxml==0.6.0         # via -r .reqs/doc.txt, nbconvert
-distlib==0.3.1            # via -r .reqs/sty.txt, virtualenv
-doc8==0.8.1               # via -r .reqs/sty.txt
-docutils==0.16            # via -r .reqs/doc.txt, -r .reqs/sty.txt, doc8, myst-nb, myst-parser, pybtex-docutils, restructuredtext-lint, rstcheck, sphinx, sphinx-book-theme, sphinx-panels, sphinx-togglebutton
-entrypoints==0.3          # via -r .reqs/doc.txt, nbconvert
-filelock==3.0.12          # via -r .reqs/sty.txt, tox, virtualenv
-flake8-blind-except==0.1.1  # via -r .reqs/sty.txt
-flake8-bugbear==20.11.1   # via -r .reqs/sty.txt
-flake8-builtins==1.5.3    # via -r .reqs/sty.txt
-flake8-polyfill==1.0.2    # via -r .reqs/sty.txt, pep8-naming
-flake8-rst-docstrings==0.0.14  # via -r .reqs/sty.txt
-flake8==3.8.4             # via -r .reqs/sty.txt, flake8-bugbear, flake8-builtins, flake8-polyfill, flake8-rst-docstrings
-gitdb==4.0.5              # via -r .reqs/doc.txt, gitpython
-gitpython==3.1.11         # via -r .reqs/doc.txt, nbdime
-graphviz==0.15            # via -r .reqs/doc.txt
-identify==1.5.10          # via -r .reqs/sty.txt, pre-commit
-idna==2.10                # via -r .reqs/doc.txt, requests
-imagesize==1.2.0          # via -r .reqs/doc.txt, sphinx
-importlib-metadata==3.1.0  # via -r .reqs/doc.txt, myst-nb
-ipykernel==5.3.4          # via -r .reqs/doc.txt, ipywidgets, jupyter, jupyter-console, notebook, qtconsole
-ipython-genutils==0.2.0   # via -r .reqs/doc.txt, -r .reqs/sty.txt, nbformat, notebook, qtconsole, traitlets
-ipython==7.19.0           # via -r .reqs/doc.txt, ipykernel, ipywidgets, jupyter-console, jupyter-sphinx, myst-nb
-ipywidgets==7.5.1         # via -r .reqs/doc.txt, jupyter, jupyter-sphinx, myst-nb
-isort==5.6.4              # via -r .reqs/sty.txt, pylint
-jedi==0.17.2              # via -r .reqs/doc.txt, ipython
-jinja2==2.11.2            # via -r .reqs/doc.txt, jupyterlab, jupyterlab-server, nbconvert, nbdime, notebook, sphinx
-json5==0.9.5              # via jupyterlab-server
-jsonschema==3.2.0         # via -r .reqs/doc.txt, -r .reqs/sty.txt, jupyterlab-server, nbformat
-jupyter-cache==0.4.1      # via -r .reqs/doc.txt, myst-nb
-jupyter-client==6.1.7     # via -r .reqs/doc.txt, ipykernel, jupyter-console, nbclient, notebook, qtconsole
-jupyter-console==6.2.0    # via -r .reqs/doc.txt, jupyter
-jupyter-core==4.7.0       # via -r .reqs/doc.txt, -r .reqs/sty.txt, jupyter-client, nbconvert, nbformat, notebook, qtconsole
-jupyter-sphinx==0.3.2     # via -r .reqs/doc.txt, myst-nb
-jupyter==1.0.0            # via -r .reqs/doc.txt
-jupyterlab-code-formatter==1.3.8  # via -r .reqs/dev.in
-jupyterlab-server==1.2.0  # via jupyterlab
-jupyterlab==2.2.9         # via -r .reqs/dev.in
-kiwisolver==1.3.1         # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, matplotlib
-labels==20.1.0            # via -r .reqs/dev.in
-latexcodec==2.0.1         # via -r .reqs/doc.txt, pybtex
-lazy-object-proxy==1.4.3  # via -r .reqs/sty.txt, astroid
-markdown-it-py==0.5.6     # via -r .reqs/doc.txt, myst-parser
-markupsafe==1.1.1         # via -r .reqs/doc.txt, jinja2
-matplotlib==3.3.3         # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt
-mccabe==0.6.1             # via -r .reqs/sty.txt, flake8, pylint
-mistune==0.8.4            # via -r .reqs/doc.txt, nbconvert
-mypy-extensions==0.4.3    # via -r .reqs/sty.txt, black, mypy
-mypy==0.790               # via -r .reqs/sty.txt
-myst-nb==0.10.1           # via -r .reqs/doc.txt
-myst-parser==0.12.10      # via -r .reqs/doc.txt, myst-nb
-nbclient==0.5.1           # via -r .reqs/doc.txt, jupyter-cache
-nbconvert==5.6.1          # via -r .reqs/doc.txt, jupyter, jupyter-sphinx, myst-nb, notebook
-nbdime==2.1.0             # via -r .reqs/doc.txt, jupyter-cache
-nbformat==5.0.8           # via -r .reqs/doc.txt, -r .reqs/sty.txt, ipywidgets, jupyter-cache, jupyter-sphinx, myst-nb, nbclient, nbconvert, nbdime, nbstripout, notebook
-nbstripout==0.3.9         # via -r .reqs/sty.txt
-nest-asyncio==1.4.3       # via -r .reqs/doc.txt, nbclient
-nodeenv==1.5.0            # via -r .reqs/sty.txt, pre-commit
-notebook==6.1.5           # via -r .reqs/doc.txt, jupyter, jupyterlab, jupyterlab-code-formatter, jupyterlab-server, nbdime, widgetsnbextension
-numpy==1.19.4             # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, matplotlib
-oset==0.1.3               # via -r .reqs/doc.txt, sphinxcontrib-bibtex
-packaging==20.4           # via -r .reqs/doc.txt, bleach, jupyterlab-code-formatter, sphinx, tox
-pandocfilters==1.4.3      # via -r .reqs/doc.txt, nbconvert
-parso==0.7.1              # via -r .reqs/doc.txt, jedi
-pathspec==0.8.1           # via -r .reqs/sty.txt, black
-pbr==5.5.1                # via -r .reqs/sty.txt, stevedore
-pep8-naming==0.11.1       # via -r .reqs/sty.txt
-pexpect==4.8.0            # via -r .reqs/doc.txt, ipython
-pickleshare==0.7.5        # via -r .reqs/doc.txt, ipython
-pillow==8.0.1             # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, matplotlib
-pip-tools==5.4.0          # via -r .reqs/dev.in
-pluggy==0.13.1            # via tox
-pre-commit==2.9.0         # via -r .reqs/sty.txt
-prometheus-client==0.9.0  # via -r .reqs/doc.txt, notebook
-prompt-toolkit==3.0.8     # via -r .reqs/doc.txt, ipython, jupyter-console
-ptyprocess==0.6.0         # via -r .reqs/doc.txt, pexpect, terminado
-py==1.9.0                 # via tox
-pybtex-docutils==0.2.2    # via -r .reqs/doc.txt, sphinxcontrib-bibtex
-pybtex==0.23.0            # via -r .reqs/doc.txt, pybtex-docutils, sphinxcontrib-bibtex
-pycodestyle==2.6.0        # via -r .reqs/sty.txt, flake8
-pycparser==2.20           # via -r .reqs/doc.txt, cffi
-pydata-sphinx-theme==0.4.1  # via -r .reqs/doc.txt, sphinx-book-theme
-pydeps==1.9.11            # via -r .reqs/doc.txt
-pydocstyle==5.1.1         # via -r .reqs/sty.txt
-pyflakes==2.2.0           # via -r .reqs/sty.txt, flake8
-pygments==2.7.2           # via -r .reqs/doc.txt, -r .reqs/sty.txt, doc8, ipython, jupyter-console, nbconvert, nbdime, qtconsole, sphinx
-pylint==2.6.0             # via -r .reqs/sty.txt
-pyparsing==2.4.7          # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, matplotlib, packaging
-pyrsistent==0.17.3        # via -r .reqs/doc.txt, -r .reqs/sty.txt, jsonschema
-python-dateutil==2.8.1    # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, jupyter-client, matplotlib
-pytoml==0.1.21            # via labels
-pytz==2020.4              # via -r .reqs/doc.txt, babel
-pyyaml==5.3.1             # via -r .reqs/doc.txt, -r .reqs/sty.txt, myst-nb, myst-parser, pre-commit, pybtex, sphinx-book-theme
-pyzmq==20.0.0             # via -r .reqs/doc.txt, jupyter-client, notebook, qtconsole
-qtconsole==5.0.1          # via -r .reqs/doc.txt, jupyter
-qtpy==1.9.0               # via -r .reqs/doc.txt, qtconsole
-regex==2020.11.13         # via -r .reqs/sty.txt, black
-requests==2.25.0          # via -r .reqs/doc.txt, jupyterlab-server, labels, nbdime, sphinx
-restructuredtext-lint==1.3.2  # via -r .reqs/sty.txt, doc8, flake8-rst-docstrings
-rstcheck==3.3.1           # via -r .reqs/sty.txt
-send2trash==1.5.0         # via -r .reqs/doc.txt, notebook
-six==1.15.0               # via -r .reqs/../requirements.txt, -r .reqs/doc.txt, -r .reqs/sty.txt, argon2-cffi, astroid, bleach, cycler, doc8, jsonschema, latexcodec, nbdime, packaging, pip-tools, pybtex, pybtex-docutils, python-dateutil, tox, virtualenv
-smmap==3.0.4              # via -r .reqs/doc.txt, gitdb
-snowballstemmer==2.0.0    # via -r .reqs/doc.txt, -r .reqs/sty.txt, pydocstyle, sphinx
-soupsieve==2.0.1          # via -r .reqs/doc.txt, beautifulsoup4
-sphinx-book-theme==0.0.39  # via -r .reqs/doc.txt
-sphinx-copybutton==0.3.1  # via -r .reqs/doc.txt
-sphinx-math-dollar==1.2   # via -r .reqs/doc.txt
-sphinx-panels==0.5.2      # via -r .reqs/doc.txt
-sphinx-thebe==0.0.8       # via -r .reqs/doc.txt
-sphinx-togglebutton==0.2.3  # via -r .reqs/doc.txt, myst-nb
-sphinx==3.3.1             # via -r .reqs/doc.txt, jupyter-sphinx, myst-nb, myst-parser, pydata-sphinx-theme, sphinx-book-theme, sphinx-copybutton, sphinx-math-dollar, sphinx-panels, sphinx-thebe, sphinx-togglebutton, sphinxcontrib-bibtex
-sphinxcontrib-applehelp==1.0.2  # via -r .reqs/doc.txt, sphinx
-sphinxcontrib-bibtex==1.0.0  # via -r .reqs/doc.txt
-sphinxcontrib-devhelp==1.0.2  # via -r .reqs/doc.txt, sphinx
-sphinxcontrib-htmlhelp==1.0.3  # via -r .reqs/doc.txt, sphinx
-sphinxcontrib-jsmath==1.0.1  # via -r .reqs/doc.txt, sphinx
-sphinxcontrib-qthelp==1.0.3  # via -r .reqs/doc.txt, sphinx
-sphinxcontrib-serializinghtml==1.1.4  # via -r .reqs/doc.txt, sphinx
-sqlalchemy==1.3.20        # via -r .reqs/doc.txt, jupyter-cache
-stdlib-list==0.8.0        # via -r .reqs/doc.txt, pydeps
-stevedore==3.2.2          # via -r .reqs/sty.txt, doc8
-terminado==0.9.1          # via -r .reqs/doc.txt, notebook
-testpath==0.4.4           # via -r .reqs/doc.txt, nbconvert
-toml==0.10.2              # via -r .reqs/sty.txt, black, pre-commit, pylint, tox
-tornado==6.1              # via -r .reqs/doc.txt, ipykernel, jupyter-client, jupyterlab, nbdime, notebook, terminado
-tox==3.20.1               # via -r .reqs/dev.in
-traitlets==5.0.5          # via -r .reqs/doc.txt, -r .reqs/sty.txt, ipykernel, ipython, ipywidgets, jupyter-client, jupyter-core, nbclient, nbconvert, nbformat, notebook, qtconsole
-typed-ast==1.4.1          # via -r .reqs/sty.txt, black, mypy
-typing-extensions==3.7.4.3  # via -r .reqs/sty.txt, black, mypy
-urllib3==1.26.2           # via -r .reqs/doc.txt, requests
-virtualenv==20.2.1        # via -r .reqs/sty.txt, pre-commit, tox
-wcwidth==0.2.5            # via -r .reqs/doc.txt, prompt-toolkit
-webencodings==0.5.1       # via -r .reqs/doc.txt, bleach
-wheel==0.35.1             # via -r .reqs/doc.txt, sphinx-togglebutton
-widgetsnbextension==3.5.1  # via -r .reqs/doc.txt, ipywidgets
-wrapt==1.12.1             # via -r .reqs/sty.txt, astroid
-zipp==3.4.0               # via -r .reqs/doc.txt, importlib-metadata
-
-# The following packages are considered to be unsafe in a requirements file:
-# pip
-# setuptools
diff --git a/requirements.txt b/requirements.txt
deleted file mode 100644
index 862364c9..00000000
--- a/requirements.txt
+++ /dev/null
@@ -1,14 +0,0 @@
-#
-# This file is autogenerated by pip-compile
-# To update, run:
-#
-#    pip-compile
-#
-cycler==0.10.0            # via matplotlib
-kiwisolver==1.3.1         # via matplotlib
-matplotlib==3.3.3         # via PWA-pages (setup.py)
-numpy==1.19.4             # via PWA-pages (setup.py), matplotlib
-pillow==8.0.1             # via matplotlib
-pyparsing==2.4.7          # via matplotlib
-python-dateutil==2.8.1    # via matplotlib
-six==1.15.0               # via cycler, python-dateutil
diff --git a/setup.cfg b/setup.cfg
index a68abac0..c176eb2d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -32,12 +32,13 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
     Topic :: Scientific/Engineering
     Topic :: Scientific/Engineering :: Physics
     Typing :: Typed
 
 [options]
-python_requires = >=3.6
+python_requires = >=3.6, <3.10
 setup_requires =
     setuptools_scm
 install_requires =
diff --git a/tox.ini b/tox.ini
index 6e0f4e5c..2a0194c0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,20 +1,17 @@
 [tox]
-passenv = PYTHONPATH
-skip_install = True
-skipsdist = True
 envlist =
     doc,
     sty,
+passenv = PYTHONPATH
+skip_install = True
 skip_missing_interpreters = True
+skipsdist = True
 
 [testenv:doc]
 description =
     Build documentation and API through Sphinx
-deps =
-    -r .reqs/doc.txt
-usedevelop = true
 changedir = docs
-whitelist_externals =
+allowlist_externals =
     make
 commands =
     make html
@@ -22,10 +19,8 @@ commands =
 [testenv:doclive]
 description =
     Set up a server to directly preview changes to the HTML pages
-deps =
-    -r .reqs/doc.txt
+allowlist_externals =
     sphinx-autobuild
-usedevelop = true
 commands =
     sphinx-autobuild \
         --watch docs \
@@ -39,11 +34,8 @@ commands =
 [testenv:linkcheck]
 description =
     Check external links in the documentation (requires internet connection)
-deps =
-    -r .reqs/doc.txt
-usedevelop = true
 changedir = docs
-whitelist_externals =
+allowlist_externals =
     make
 commands =
     make ignore-warnings=1 linkcheck  # for margin directive
@@ -51,35 +43,33 @@ commands =
 [testenv:sty]
 description =
     Perform all linting, formatting, and spelling checks
-deps =
-    -r .reqs/sty.txt
-usedevelop = true
 setenv =
     SKIP = mypy
-whitelist_externals =
+allowlist_externals =
     bash
+    mypy
+    pre-commit
 commands =
-    mypy .  # run separately because of potential caching problems
+    mypy src .  # run separately because of potential caching problems
     pre-commit run {posargs} -a
-    - bash -ec "cspell $(git ls-files)"
+    - bash -ec "cspell --no-progress $(git ls-files)"
 
 [testenv:upgrade]
 description =
-    Upgrade pinned dependencies
+    Upgrade pinned dependencies for native Python version
+allowlist_externals =
+    bash
 deps =
     pip-tools
-skip_install = true
 commands =
-    pip-compile --upgrade
-    pip-compile --upgrade .reqs/doc.in
-    pip-compile --upgrade .reqs/sty.in
-    pip-compile --upgrade .reqs/dev.in -o requirements-dev.txt
+    bash reqs/upgrade.sh
 
 [flake8]
 application-import-names =
     pwa_pages
 filename =
     ./src/*.py
+    ./tests/*.py
 exclude =
     __pycache__
     docs/conf.py