have : ord_sgn (compare n m) ≃ (0:Difference ℕ) := ‹sgn (n——m) ≃ 0›
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : (n——m).sgn ≃ 0
⊢ n——m ≃ 0
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : (n——m).sgn ≃ 0
this : ord_sgn (compare n m) ≃ 0
⊢ n——m ≃ 0