have h3 := good_special_equality h (mul_inv_cancel <| sub_ne_zero_of_ne h2)
R : Type u_1
D : Type u_2
inst✝ : DivisionRing D
f : D → D
h : good f
h0 : f ≠ 0
c : D
h1 : f c = 0
h2 : ¬c = 1
⊢ f = 0
R : Type u_1
D : Type u_2
inst✝ : DivisionRing D
f : D → D
h : good f
h0 : f ≠ 0
c : D
h1 : f c = 0
h2 : ¬c = 1
h3 : f (f (c - 1 + 1) * f ((c - 1)⁻¹ + 1)) = 0
⊢ f = 0