∀ {G : Type u_1} [inst : AddGroup G] [inst_1 : TopologicalSpace G] {H : Type u_2} [inst_2 : AddGroup H]
  [inst_3 : TopologicalSpace H] (U : OpenAddSubgroup G) (V : OpenAddSubgroup H), IsOpen (↑U ×ˢ ↑(↑V).toAddSubmonoid)