proposition: Lemma close_sym x y : close x y -> close y x.
proof: Proof. by rewrite !closeEnbhs /cluster/= meetsC. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed