proposition: Lemma open_subsetE (A B : set T) : open A -> (A `<=` B) = (A `<=` B^°).
proof: Proof. rewrite openE => Aop; rewrite propeqE; split. by move=> sAB p Ap; apply: filterS sAB _; apply: Aop. by move=> sAB p /sAB /interior_subset. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed