proposition: Lemma topologydirprod_htrue : ∏ x : U × V, isfilter_htrue (topologydirprod x).
proof: Proof. intros z. apply hinhpr. exists (λ _, htrue), (λ _, htrue). repeat split. - apply isOpen_htrue. - apply isOpen_htrue. Qed.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.Topology.Filters UniMath.Algebra.Groups UniMath.Algebra.DivisionRig UniMath.Algebra.ConstructiveStructures