Formal definition[edit]
Formally, an intersection graph is an undirected graph formed from a family of sets
Si, i = 0, 1, 2, ...
by creating one vertex vi for each set Si, and connecting two vertices vi and vj by an edge whenever the corresponding two sets have a nonempty intersection, that is,
E(G) = {{vi, vj} | Si ∩ Sj ≠ ∅}.