∀ {F : Type u_1} {G : Type u_2} {N : Type u_3} [inst : SubtractionMonoid G] [inst_1 : AddMonoid N]
  [inst_2 : FunLike F G N] [AddMonoidHomClass F G N] {x : G}, IsAddUnit x → ∀ (f g : F), f x = g x → f (-x) = g (-x)