# Arboricity

Let G=(V,E) be an undirected graph. For a node set $X \subseteq V$, $i_G(X)$ denotes the number of induced edges in X. The arboricity of G is
$\mbox{arb}(G)=\max_{X \subseteq V, |X| \geq 2} \frac{i_G(X)}{|X|-1}.$