Graph theory lemma
Trivia · proposed by @vipproaccout
In graph theory, what is this lemma called?
In any finite undirected graph $G=(V,E)$, the sum of the degrees of all vertices equals twice the number of edges:
$$\sum_{v\in V}\deg(v)=2|E|.$$
AMantel's lemma
BTuran's lemma
CBrooks' lemma
DHandshake's lemma