proposition: Lemma accessible_closed_set1 : accessible_space -> forall x, closed [set x].
proof: Proof. move=> T1 x; rewrite -[X in closed X]setCK; apply: open_closedC. rewrite openE => y /eqP /T1 [U [oU [yU xU]]]. rewrite /interior nbhsE /=; exists U; last by rewrite subsetC1. by split=> //; exact: set_mem. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed