∀ (R : Type u_1) [inst : CommRing R] (n m k : ℕ) (hn : n = m + k)
  (s : TensorProduct R (MvPolynomial (Fin m) R) (MvPolynomial (Fin k) R)),
  (MvPolynomial.aeval (Sum.elim (fun x => MvPolynomial.X x ⊗ₜ[R] 1) fun x => 1 ⊗ₜ[R] MvPolynomial.X x))
      ((MvPolynomial.map MvPolynomial.C) ((MvPolynomial.tensorEquivSum R (Fin m) (Fin k) R) s)) =
    s