Strong perfect graph theorem

The Strong Perfect Graph Theorem, proved by Maria Chudnovsky, Neil Robertson, Paul Seymour, and Robin Thomas in 2006, establishes an important characterization of perfect graphs. The theorem states that a graph is perfect if and only if it contains no induced subgraph that is an odd cycle of length at least 5 or the complement of such a cycle (i.e., a complete graph minus an odd cycle).