proposition: Lemma fproj_rot p : simple p -> fproj (rot n0 p) =1 fproj p.
proof: Proof. move=> Up x; have [pFx | pF'x] := boolP (x \in fband p); last first. by rewrite /fproj !nth_default // leqNgt -has_find // has_rot. case/fprojP: pFx; move: (fproj p x) => y py xFy. by rewrite (fproj_cface _ xFy) simple_fproj ?simple_rot ?mem_rot. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan)