∀ {R : Type r} [inst : CommRing R] {W' : WeierstrassCurve.Affine R} (x y ℓ : R),
  (WeierstrassCurve.Affine.CoordinateRing.mk W') (Polynomial.C (W'.addPolynomial x y ℓ)) =
    (WeierstrassCurve.Affine.CoordinateRing.mk W')
      ((Polynomial.X - Polynomial.C (WeierstrassCurve.Affine.linePolynomial x y ℓ)) *
        (W'.negPolynomial - Polynomial.C (WeierstrassCurve.Affine.linePolynomial x y ℓ)))