proposition: Lemma principal_filterP {X} (x : X) (W : set X) : principal_filter x W <-> W x.
proof: Proof. by split=> [|? ? ->]; [exact|]. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed