proposition: Lemma merge_union_bwd_hom : {homo merge_union_bwd : x y / x = y %[mod merge_union_rel] >-> x = y %[mod e]}.
proof: Proof. move => x y /eqquotP. rewrite map_equivE. by move/eqquotP. Qed.
imports: HB(structures) Coq(Setoid CMorphisms) mathcomp(all_ssreflect) GraphTheory(preliminaries bij)