∀ {M : Type u_1} {α : Type u_2} [inst : AddGroup M] [inst_1 : AddAction M α] {s t : Set α},
  SubAddAction.fixingAddSubgroup_union_to_fixingAddSubgroup_of_fixingAddSubgroup =
    { toFun := fun m => ⟨⟨↑m, ⋯⟩, ⋯⟩, map_zero' := ⋯, map_add' := ⋯ }