∀ {σ : Type u_1} {τ : Type u_2} {R : Type u_3} [inst : CommSemiring R] (p : ℕ) (f : σ → MvPolynomial τ R)
  (φ : MvPolynomial σ R),
  (MvPolynomial.expand p) ((MvPolynomial.bind₁ f) φ) = (MvPolynomial.bind₁ fun i => (MvPolynomial.expand p) (f i)) φ