proposition: Lemma closeE x y : close x y = (x = y).
proof: Proof. rewrite propeqE; split; last by move=> ->; exact: close_refl. by rewrite closeEnbhs; exact: sep. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed