Erdős Problem 1068 #
Reference: erdosproblems.com/1068
theorem
Erdos1068.erdos_1068 :
sorry ↔ ∀ (V : Type) (G : SimpleGraph V),
↑G.chromaticNumber = Cardinal.aleph 1 → ∃ (s : Set V), s.Countable ∧ (SimpleGraph.induce s G).InfinitelyConnected
Does every graph with chromatic number $\aleph_1$ contain a countable subgraph which is infinitely connected?