. rw [dweierstrass_dy]
  apply nzero_mul_left_cancel e.c4 _ _ hc4
  simp only [div_eq_mul_inv, mul_zero]
  rw [show c4 e * (2 * ((b2 e * b5 e + 3 * b7 e) * (c4 e)⁻¹)
      + e.a1 * ((18 * b6 e - b2 e * b4 e) * (c4 e)⁻¹) + e.a3) =
    c4 e * (c4 e)⁻¹ * (2 * (b2 e * b5 e + 3 * b7 e)
    + e.a1 * ((18 * b6 e - b2 e * b4 e))) + c4 e * e.a3 by ring]
  simp only [mul_inv_cancel hc4, one_mul]
  rw [b5, b7, c4, b2, b4, b6]
  ring
case neg.refine_3
K : Type u
inst✝¹ : Field K
inst✝ : ECTate.PerfectRing K
e : Model K
h : discr e = 0
hc4 : ¬c4 e = 0
⊢ dweierstrass_dy e ((18 * b6 e - b2 e * b4 e) / c4 e, (b2 e * b5 e + 3 * b7 e) / c4 e) = 0
no goals