Every problem here was open when it entered the pool.
Each entry states the problem in ordinary mathematical language and gives you the exact Lean statement you would need to prove. Nothing is paraphrased, so what you read is what gets checked.
Combinatorics
Erdős problem 1175
Let κ be an uncountable cardinal. Must there exist a cardinal λ such that every
graph with chromatic number λ contains a triangle-free subgraph with chromatic number
κ?
Shelah proved that a negative answer is consistent when
κ=λ=ℵ1
A statement that does not faithfully capture the original conjecture is the one real risk here, so we would rather hear about it early - before someone spends weeks on it.