∀ {X : Type u_1} {R : Type u_2} [inst : Zero X] [inst_1 : TopologicalSpace X] [inst_2 : TopologicalSpace R]
  [inst_3 : AddCommMonoid R] [inst_4 : ContinuousAdd R] (a b c : ContinuousMapZero X R), a + b + c = a + (b + c)