fact: Definition next_hat h0 p := match p with | Pnil => h0 | Pcons _ h _ => h | Pcons6 h _ _ => h | Pcons7 h _ _ _ => h | Pcons8 h _ _ _ _ => h end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap color geometry)