∀ {M : Type u_1} {N : Type u_2} {α : Type u_5} [inst : SMul M α] [inst_1 : SMul Mᵐᵒᵖ α] [IsCentralScalar M α]
  [inst_3 : SMul M N] [inst_4 : SMul Mᵐᵒᵖ N] [IsCentralScalar M N] [inst_6 : SMul N α] [IsScalarTower M N α],
  IsScalarTower Mᵐᵒᵖ N α