∀ {G : Type u_1} {α : Type u_2} [inst : AddGroup G] [inst_1 : AddAction G α] (g : G) (a : α),
  AddAction.stabilizer G (g +ᵥ a) =
    AddSubgroup.map (AddEquiv.toAddMonoidHom (Additive.toMul (AddAut.conj g))) (AddAction.stabilizer G a)