have : step (n + m) ≃ step n + m := Rel.symm Addition.step_add
case h
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n✝ m n : ℕ
x✝ : step n + m ≃ 0
⊢ False
case h
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n✝ m n : ℕ
x✝ : step n + m ≃ 0
this : step (n + m) ≃ step n + m
⊢ False