Dependent random choice
= Dependent random choice
{wiki}
Dependent random choice finds a large vertex set whose small subsets have large common neighbourhoods. In a bipartite graph with parts $A,B$, choose random vertices of $B$ with repetition and take their common neighbourhood $X\subseteq A$; convexity gives a lower bound for $\mathbb E|X|$, while counting subsets of $X$ with small common neighbourhood allows their deletion.