Local/global reasons for high chromaticity.
Notions of clique and independence number.
Definition of perfect graphs, with justification (3:50-6:00).
Motivation and statement of strong perfect graph theorem (from 8:30).
Characterising graph properties by excluding subgraphs, minors etc (from 9:30).
A secret about infinite graphs (11:00).
Statement of weak perfect graph theorem, Theorem 5.5.4 (12:55).
Replication lemma with proof (14:45-25:00).
Proof of weak perfect graph theorem from 27:47.
Covers most of Chapter 5.5.
Based on R.Diestel, Graph Theory, Springer GTM173, 6th edition 2025.
Ebooks available at https://diestel-graph-theory.com under links "Standard eBook" and "Professional Edition".
