proposition: Lemma closed_subspaceT : closed (A : set (subspace A)).
proof: Proof. rewrite -(setCK A); by apply: open_closedC; rewrite -open_subspaceIT setICl; exact: open0. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed