Hypergraph codegree
= Hypergraph codegree
{title2=$d_H(\sigma)=|\{e:\sigma\subseteq e\}|$}
= Codegree
{synonym}
The codegree of a vertex set $\sigma$ in a <hypergraph> is the number of hyperedges containing every vertex in $\sigma$. For a singleton this is the <hypergraph vertex degree>; for two vertices it measures how often those vertices occur together. Subset codegrees of all sizes control the overlap relevant to the <hypergraph container theorem>.