∀ {R : Type r} [inst : CommRing R] {W : WeierstrassCurve.Affine R} [Nontrivial R] [WeierstrassCurve.IsElliptic W]
  {x y : R}, (WeierstrassCurve.toAffine W).Equation x y ↔ (WeierstrassCurve.toAffine W).Nonsingular x y