proposition: Lemma fct_ent_inv A : fct_ent A -> fct_ent (A^-1)%classic.
proof: Proof. move=> [B entB sBA]; exists (B^-1)%classic; first exact: entourage_inv. by move=> fg Bgf; apply/sBA. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed