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Add Erdős Problem 1168 (ℵ_{ω+1} partition without GCH)#3792

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Add Erdős Problem 1168 (ℵ_{ω+1} partition without GCH)#3792
henrykmichalewski wants to merge 4 commits into
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henrykmichalewski:add-problem-1168

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Formalizes Erdős Problem 1168 on a partition relation for ℵ_{ω+1} that does not assume GCH.

Contents

  • New definition CardinalCountableColorRamsey κ: generalizes the partition statement to ℵ_0 colors.
  • The main open theorem statement for Problem 1168.
  • An under_GCH variant relating the statement to its form under the Generalized Continuum Hypothesis.
  • Four proved sanity checks verifying expected behavior of the defined relation.

Closes #1992

Assisted by Claude (Anthropic).

@github-actions github-actions Bot added the erdos-problems Erdős Problems label Apr 17, 2026
Mirrors the Round C docstring pass from the private repo's
phase1-infrastructure branch. Each Lean file now carries the
canonical source statement and upstream URL inline so reviewers
can verify formalization against the source without navigating
away from the diff.
**Status**: OPEN.
-/
@[category research open, AMS 5]
theorem erdos_1168 : CardinalCountableColorRamsey (ℵ_ (ω + 1)) := by
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Does the source ask to prove the negative partition relation ℵ_{ω+1} ↛ ... without GCH? The quoted text has \not\to, but this theorem states the positive CardinalCountableColorRamsey. Could you negate the relation here, or rename this as the positive predicate and make the main theorem ¬ CardinalCountableColorRamsey ...?

@Paul-Lez Paul-Lez added the awaiting-author The author should answer a question or perform changes. Reply when done. label May 7, 2026
Per Paul-Lez's review, the source asserts the NOT-arrow
$\aleph_{\omega+1}\not\to(\aleph_{\omega+1},3,…)^2_{\aleph_0}$, but the
headline previously stated the positive `CardinalCountableColorRamsey`.
Negate it (and the matching `under_GCH` known-result variant for
consistency).
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Thanks for the review @PaulLez. Pushed 82bfdfd on add-problem-1168: negated the partition relation in the headline (now ¬ CardinalCountableColorRamsey (ℵ_ (ω + 1))) so it matches the source's $\not\to$. For consistency, also negated the matching under_GCH known-result variant since the Erdős–Hajnal–Rado [EHR65] result establishes the negative arrow under GCH.

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Erdős Problem 1168: Partition Relation for ℵ_{ω+1} Without GCH

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