proposition: Lemma freshP' (E E' : {fset nat}) : E' `<=` E -> fresh E \notin E'.
proof: Proof. apply: contraTN => H. apply/fsubsetPn. exists (fresh E) => //. exact: freshP. 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)