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[Merged by Bors] - feat(measure_theory/order/upper_lower): Order-connected sets in ℝⁿ are measurable #16976

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@YaelDillies YaelDillies commented Oct 14, 2022

Prove that the frontier of an order-connected set in ℝⁿ (with the -metric, but it doesn't actually matter) has measure zero.

As a corollary, antichains in ℝⁿ have measure zero.

Co-authored-by: @JasonKYi


This is a three lines remark in Reverse Kleitman Inequalities, Bollobas, Leader, Radcliffe, with no proof. So Jason, Bhavik and I came up with a proof using Lebesgue Density Theorem.

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@YaelDillies YaelDillies added awaiting-review The author would like community review of the PR blocked-by-other-PR This PR depends on another PR which is still in the queue. A bot manages this label via PR comment. t-order Order hierarchy t-measure-probability Measure theory / Probability theory labels Oct 14, 2022
@YaelDillies YaelDillies requested a review from a team as a code owner October 14, 2022 08:42
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@bors bors bot changed the title feat(measure_theory/order/upper_lower): Order-connected sets in ℝⁿ are measurable [Merged by Bors] - feat(measure_theory/order/upper_lower): Order-connected sets in ℝⁿ are measurable Oct 16, 2023
@bors bors bot closed this Oct 16, 2023
@bors bors bot deleted the ord_connected_measurable branch October 16, 2023 12:40
eric-wieser pushed a commit that referenced this pull request Oct 16, 2023
…are measurable (#16976)

Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero.

As a corollary, antichains in `ℝⁿ` have measure zero.

Co-authored-by: @JasonKYi
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Feb 14, 2024
* Add `upperBounds_closure`, `lowerBounds_closure`, `bddAbove_closure`, `bddBelow_closure`.
* Add `IsAntichain.interior_eq_empty`.
* Generalize `nhds_left'_le_nhds_ne` and `nhds_right'_le_nhds_ne` to a `Preorder`.

Partly forward-ports leanprover-community/mathlib3#16976
riccardobrasca pushed a commit to leanprover-community/mathlib4 that referenced this pull request Feb 18, 2024
* Add `upperBounds_closure`, `lowerBounds_closure`, `bddAbove_closure`, `bddBelow_closure`.
* Add `IsAntichain.interior_eq_empty`.
* Generalize `nhds_left'_le_nhds_ne` and `nhds_right'_le_nhds_ne` to a `Preorder`.

Partly forward-ports leanprover-community/mathlib3#16976
dagurtomas pushed a commit to leanprover-community/mathlib4 that referenced this pull request Mar 22, 2024
* Add `upperBounds_closure`, `lowerBounds_closure`, `bddAbove_closure`, `bddBelow_closure`.
* Add `IsAntichain.interior_eq_empty`.
* Generalize `nhds_left'_le_nhds_ne` and `nhds_right'_le_nhds_ne` to a `Preorder`.

Partly forward-ports leanprover-community/mathlib3#16976
YaelDillies added a commit to leanprover-community/mathlib4 that referenced this pull request Mar 23, 2024
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Mar 23, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
utensil pushed a commit to leanprover-community/mathlib4 that referenced this pull request Mar 26, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
Louddy pushed a commit to leanprover-community/mathlib4 that referenced this pull request Apr 15, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
atarnoam pushed a commit to leanprover-community/mathlib4 that referenced this pull request Apr 16, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
uniwuni pushed a commit to leanprover-community/mathlib4 that referenced this pull request Apr 19, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
callesonne pushed a commit to leanprover-community/mathlib4 that referenced this pull request Apr 22, 2024
Partially forward-port leanprover-community/mathlib3#16976

Also fix an unused argument that somehow made it to master, likely from #10661.
chenjulang added a commit to chenjulang/mathlib that referenced this pull request May 11, 2024
* commit '65a1391a0106c9204fe45bc73a039f056558cb83': (12443 commits)
  feat(data/{list,multiset,finset}/*): `attach` and `filter` lemmas (leanprover-community#18087)
  feat(combinatorics/simple_graph): More clique lemmas (leanprover-community#19203)
  feat(measure_theory/order/upper_lower): Order-connected sets in `ℝⁿ` are measurable (leanprover-community#16976)
  move old README.md to OLD_README.md
  doc: Add a warning mentioning Lean 4 to the readme (leanprover-community#19243)
  feat(topology/metric_space): diameter of pointwise zero and addition (leanprover-community#19028)
  feat(topology/algebra/order/liminf_limsup): Eventual boundedness of neighborhoods (leanprover-community#18629)
  feat(probability/independence): Independence of singletons (leanprover-community#18506)
  feat(combinatorics/set_family/ahlswede_zhang): Ahlswede-Zhang identity, part I (leanprover-community#18612)
  feat(data/finset/lattice): `sup'`/`inf'` lemmas (leanprover-community#18989)
  chore(order/liminf_limsup): Generalise and move lemmas (leanprover-community#18628)
  feat(algebraic_topology/dold_kan): The Dold-Kan equivalence for abelian categories (leanprover-community#17926)
  feat(data/sum/interval): The lexicographic sum of two locally finite orders is locally finite (leanprover-community#11352)
  feat(analysis/convex/proj_Icc): Extending convex functions (leanprover-community#18797)
  feat(algebraic_topology/dold_kan): The Dold-Kan equivalence for pseudoabelian categories (leanprover-community#17925)
  feat(measure_theory/measure/haar_quotient): the Unfolding Trick (leanprover-community#18863)
  feat(linear_algebra/orientation): add `orientation.reindex` (leanprover-community#19236)
  feat(combinatorics/quiver/covering): Definition of coverings and unique lifting of paths (leanprover-community#17828)
  feat(set_theory/game/pgame): small sets of pre-games / games / surreals are bounded (leanprover-community#15260)
  feat(tactic/positivity): Extension for `ite` (leanprover-community#17650)
  ...

# Conflicts:
#	README.md
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 7, 2024
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 7, 2024
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 7, 2024
YaelDillies added a commit to leanprover-community/mathlib4 that referenced this pull request Jun 8, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
YaelDillies added a commit to leanprover-community/mathlib4 that referenced this pull request Jun 17, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
mathlib-bors bot pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 18, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
AntoineChambert-Loir pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 20, 2024
AntoineChambert-Loir pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 20, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
grunweg pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 20, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
kbuzzard pushed a commit to leanprover-community/mathlib4 that referenced this pull request Jun 26, 2024
Prove that the frontier of an order-connected set in `ℝⁿ` (with the `∞`-metric, but it doesn't actually matter) has measure zero. As a corollary, antichains in `ℝⁿ` have measure zero.

This is not so trivial as one might think. The proof Kexing and I came up with involves the Lebesgue density theorem.

Partially forward-port leanprover-community/mathlib3#16976
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6 participants