calc
  compare n m
    = _ := ‹compare n m = Ordering.eq›
  Ordering.eq
    = _ := Eq.symm ‹compare (n + k) (m + k) = Ordering.eq›
  compare (n + k) (m + k)
    = _ := rfl
ℕ : Type
inst✝⁴ : Core ℕ
inst✝³ : Induction ℕ
inst✝² : Addition ℕ
inst✝¹ : Sign ℕ
order_inst : Order ℕ
inst✝ : Compare ℕ
n m k : ℕ
tri : AA.OneOfThree (n < m) (n ≃ m) (n > m)
b✝ : n ≃ m
this✝¹ : compare n m = Ordering.eq
this✝ : n + k ≃ m + k
this : compare (n + k) (m + k) = Ordering.eq
⊢ compare n m = compare (n + k) (m + k)
no goals