Extremal Graph Theory and Ramsey Theory · Superchallenge problem

Refinement: if $R(s-1,t)$ and $R(s,t-1)$ are BOTH even, then $R(s,t)\le R(s-1,t)+R(s,t-1)-1$. Apply it with $R(2,4)=4$ and $R(3,3)=6$ to bound $R(3,4)$.