Two-graphs

Abstract

A clique of a two-graph (V,∆) is a subset C of V such that every triple from C is in ∆. The two-graphs (V,∆) and (V ′,∆′) are isomorphic if there is a bijection V → V ′ that induces a bijection ∆→ ∆′. The automorphism group Aut(V,∆) of a two-graph (V,∆) is the group of permutations of V that preserve ∆.