proposition: Lemma open_subspaceW (U : set T) : open (U : set T) -> open (U : set (subspace A)).
proof: Proof. by move=> oU; apply/open_subspaceP; exists U. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed