A new class of perfect Hoàng graphs

A Hoàng graph G = (V, E) is a graph whose edges may be coloured with two colours (red and white) such that no induced path on four vertices has wings of the same colour. Hoàng (1995) conjectured that these graphs are perfect and proved two partial results concerning their perfectness. We use here a different technique to establish that for reducible Hoàng graphs this conjecture is true.