calc
  n + step d   ≃ _ := add_step
  step (n + d) ≃ _ := AA.subst₁ ‹n + d ≃ m›
  step m       ≃ _ := Rel.refl
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝ : n ≤ m
d : ℕ
h✝ : n + d ≃ m
⊢ n + step d ≃ step m
no goals