proposition: Lemma size_drop_part n p : size_part (drop_part n p) = size_part p - n.
proof: Proof. by elim: n p => [|n IHn] []. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap color geometry)