Erdős Problem 595 (250): Is there an infinite graph G which contains no $K_4$ and is not the union of countably many triangle-free graphs?

**The complete graph ⊤ on Fin 4 is not $K_4$-free**: ⊤ on Fin 4 equals the complete graph $K_4$, so it contains $K_4$ as a subgraph and is not $K_4$-free.

This sanity check confirms the $K_4$-free hypothesis of Problem 595 is non-trivial.