In graph theory, the perfect graph theorem of László Lovász (1972a, 1972b) states that an undirected graph is perfect if and only if its complement graph is also perfect. This result had been conjectured by Berge (1961, 1963), and it is sometimes called the weak perfect graph theorem to distinguish it from the strong perfect graph theorem[1] characterizing perfect graphs by their forbidden induced subgraphs.
- ^ This was also conjectured by Berge but only proven much later by Chudnovsky et al. (2006).