∀ {F : Type u} [inst : Field F] {W : WeierstrassCurve.Affine F} [inst_1 : DecidableEq F] {x₁ y₁ : F}
  {h₁ : W.Nonsingular x₁ y₁} (hy : y₁ ≠ W.negY x₁ y₁),
  WeierstrassCurve.Affine.Point.some x₁ y₁ h₁ + WeierstrassCurve.Affine.Point.some x₁ y₁ h₁ =
    WeierstrassCurve.Affine.Point.some (W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₁)) (W.addY x₁ x₁ y₁ (W.slope x₁ x₁ y₁ y₁)) ⋯