Lemmify

Lemmify is a library for typesetting mathematical theorems in typst. It aims to be easy to use while trying to be as flexible and idiomatic as possible. This means that the interface might change with updates to typst (for example if user-defined element functions are introduced). But no functionality should be lost.

Basic Usage

To get started with Lemmify, follow these steps:

1. Import the Lemmify library:

#import "@preview/lemmify:0.1.4": *

2. Define the default styling for a few default theorem types:

#let (
  theorem, lemma, corollary,
  remark, proposition, example,
  proof, rules: thm-rules
) = default-theorems("thm-group", lang: "en")

3. Apply the generated styling:

#show: thm-rules

4. Create theorems, lemmas, and proofs using the defined styling:

#theorem(name: "Some theorem")[
  Theorem content goes here.
]<thm>

#proof[
  Complicated proof.
]<proof>

@proof and @thm[theorem]

5. Customize the styling further using show rules. For example, to add a red box around proofs:

#show thm-selector("thm-group", subgroup: "proof"): it => box(
  it,
  stroke: red + 1pt,
  inset: 1em
)

The result should now look something like this:

Useful examples

If you do not want to reset the theorem counter on headings you can use the max-reset-level parameter:

default-theorems("thm-group", max-reset-level: 0)

It specifies the highest level at which the counter is reset. To manually reset the counter you can use the thm-reset-counter function.

---

By specifying numbering: none you can create unnumbered theorems.

#example(numbering: none)[
  Some example.
]

To make all examples unnumbered you could use the following code:

#let example = example.with(numbering: none)

---

To create other types (or subgroups) of theorems you can use the new-theorems function.

#let (note, rules) = new-theorems("thm-group", ("note": text(red)[Note]))
#show: rules

If you have already defined custom styling you will notice that the newly created theorem does not use it. You can create a dictionary to make applying it again easier.

#let my-styling = (
  thm-styling: thm-styling-simple,
  thm-numbering: ..,
  ref-styling: ..
)

#let (note, rules) = new-theorems("thm-group", ("note": "Note), ..my-styling)

---

By varying the group parameter you can create independently numbered theorems:

#let (
  theorem, proof,
  rules: thm-rules-a
) = default-theorems("thm-group-a")
#let (
  definition,
  rules: thm-rules-b
) = default-theorems("thm-group-b")

#show: thm-rules-a
#show: thm-rules-b

---

To specify parameters of the styling functions the .with function is used.

#let (
  theorem,
  rules: thm-rules
) = default-theorems(
  "thm-group",
  thm-numbering: thm-numbering-heading.with(max-heading-level: 2)
)

Example

#import "@preview/lemmify:0.1.4": *

#let my-thm-style(
  thm-type, name, number, body
) = grid(
  columns: (1fr, 3fr),
  column-gutter: 1em,
  stack(spacing: .5em, strong(thm-type), number, emph(name)),
  body
)

#let my-styling = (
  thm-styling: my-thm-style
)

#let (
  theorem, rules
) = default-theorems("thm-group", lang: "en", ..my-styling)
#show: rules
#show thm-selector("thm-group"): box.with(inset: 1em)

#lorem(20)
#theorem[
  #lorem(40)
]
#lorem(20)
#theorem(name: "Some theorem")[
  #lorem(30)
]

Documentation

The two most important functions are:

default-theorems: Create a default set of theorems based on the given language and styling.

• group: The group id.
• lang: The language to which the theorems are adapted.
• thm-styling, thm-numbering, ref-styling: Styling parameters are explained in further detail in the Styling section.
• proof-styling: Styling which is only applied to proofs.
• max-reset-level: The highest heading level on which theorems are still reset.

new-theorems: Create custom sets of theorems with the given styling.

• group: The group id.
• subgroup-map: Mapping from group id to some argument. The simple styles use thm-type as the argument (ie "Beispiel" or "Example" for group id "example")
• thm-styling, thm-numbering, ref-styling, ref-numbering: Styling which to apply to all subgroups.

---

use-proof-numbering: Decreases the numbering of a theorem function by one. See Styling for more information.

---

thm-selector: Returns a selector for all theorems of the specified group. If subgroup is specified, only the theorems belonging to it will be selected.

---

There are also a few functions to help with resetting counters.

thm-reset-counter: Reset theorem group counter manually. Returned content needs to added to the document.

thm-reset-counter-heading-at: Reset theorem group counter at headings of the specified level. Returns a rule that needs to be shown.

thm-reset-counter-heading: Reset theorem group counter at headings of at most the specified level. Returns a rule that needs to be shown.

Styling parameters

If possible the best way to adapt the look of theorems is to use show rules as shown above, but this is not always possible. For example if we wanted theorems to start with 1.1 Theorem instead of Theorem 1.1. You can provide the following functions to adapt the look of the theorems.

---

thm-styling: A function: (arg, name, number, body) -> content, that allows you to define the styling for different types of theorems. Below only the arg will be specified.

Pre-defined functions

• thm-style-simple(thm-type): thm-type num (name) body
• thm-style-proof(thm-type): thm-type num (name) body □
• thm-style-reversed(thm-type): num thm-type (name) body

---

thm-numbering: A function: figure -> content, that determines how theorems are numbered.

Pre-defined functions: (Assume heading is 1.1 and theorem count is 2)

• thm-numbering-heading: 1.1.2
  • max-heading-level: only use the a limited number of subheadings. In this case if it is set to 1 the result would be 1.2 instead.
• thm-numbering-linear: 2
• thm-numbering-proof: No visible content is returned, but the counter is reduced by 1 (so that the proof keeps the same count as the theorem). Useful in combination with use-proof-numbering to create theorems that reference the previous theorem (like proofs).

---

ref-styling: A function: (arg, thm-numbering, ref) -> content, to style theorem references.

Pre-defined functions:

• thm-ref-style-simple(thm-type)
  • @thm -> thm-type 1.1
  • @thm[custom] -> custom 1.1

---

ref-numbering: Same as thm-numbering but only applies to the references.

Roadmap

• More pre-defined styles.
  • Referencing theorems by name.
• Support more languages.
• Better documentation.
• Outlining theorems.

If you are encountering any bugs, have questions or are missing features, feel free to open an issue on Github.

Changelog

• Version 0.1.4

  • Fix error on unnamed theorems

• Version 0.1.3

  • Allow "1.1." numbering style by default
  • Ignore unnumbered subheadings
  • Add max-heading-level parameter to thm-numbering-heading
  • Adapt lemmify to typst version 0.8.0

• Version 0.1.2

  • Better error message on unnumbered headings
  • Add Italian translations (@porcaror)

• Version 0.1.1

  • Add Dutch translations (@BroodjeKroepoek)
  • Add French translations (@MDLC01)
  • Fix size of default styles and make them breakable