proposition: Lemma pIO_fresh (isG : is_graph G) x : x \notin vset G -> x \notin pIO.
proof: Proof. apply: contraNN. rewrite !inE. case/orP => /eqP ->; [exact: p_inP|exact: p_outP]. Qed.
imports: HB(structures) Coq(Relation_Definitions Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij equiv) GraphTheory(setoid_bigop structures pttdom rewriting) GraphTheory(finmap_plus)