  Roussel and Rubio proved a lemma which is essential in the proof of the
Strong Perfect Graph Theorem. We give a new short proof of the main case of
this lemma. In this note, we also give a short proof of Hayward's decomposition
theorem for weakly chordal graphs, relying on a Roussel--Rubio-type lemma. We
recall how Roussel--Rubio-type lemmas yield very short proofs of the existence
of even pairs in weakly chordal graphs and Meyniel graphs.
