Bichromatic P 4 -composition schemes for perfect orderability

摘要: A P4 is an induced path with four vertices. bichromatic composition scheme as follows: (1) start two graphs vertex sets of different colour, say black • and white ∘, (2) select a set allowable four-vertex sequences, for example {••••, ∘∘∘∘, •∘∘•, ∘••∘}, (3) add edges between the so that in composed graph each coloured sequence. Answering question Chvatal, we determine all such schemes which preserve perfect orderability.