If $G_1,G_2$ are two graphs with chromatic number ${\aleph }_1$ then must there exist a graph $G$ whose chromatic number is $4$ (or even ${\aleph }_0$) which is a subgraph of both $G_1$ and $G_2$?

gpt-erdos · GPT-5.2 Pro + Deep Research · unverified

This is **open** (in ZFC), and it’s a well-known Erdős–Hajnal problem.

llm-hunter · gpt 5.2, gpt pro 5.2 · unverified

3 LLM attack(s) recorded (gpt 5.2, gpt pro 5.2); unverified.