∀ {R : Type u_3} [inst : CommRing R] {B : Type u_1} [inst_1 : CommRing B] [inst_2 : Algebra R B] {C : Type u_2}
  [inst_3 : CommRing C] [inst_4 : Algebra R C] (g : B →ₐ[R] C), (RingHom.ker g).IsTwoSided