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FormalConjectures.ErdosProblems.«623»

Erdős Problem 623 #

Reference: erdosproblems.com/623

theorem Erdos623.erdos_623 :
(∀ (X : Type u), Cardinal.mk X = Cardinal.aleph Ordinal.omega0∀ (f : Finset XX), (∀ (A : Finset X), f AA)∃ (Y : Set X), Y.Infinite ∀ (B : Finset X), B Yf BY) sorry

Let $X$ be a set of cardinality $\aleph_\omega$ and $f$ be a function from the finite subsets of $X$ to $X$ such that $f(A)\not\in A$ for all $A$. Must there exist an infinite $Y\subseteq X$ that is independent - that is, for all finite $B\subset Y$ we have $f(B)\not\in Y$?