proposition: Lemma open_subspaceT : open (A : set (subspace A)).
proof: Proof. by move=> ?; case: nbhs_subspaceP => //= ? ?; apply: withinT. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed