apply Iff.intro
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
neg_diff : ∀ {k : ℕ}, 0——k ≃ -1 * coe k
⊢ Negative (n——m) ↔ n < m
case mp
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
neg_diff : ∀ {k : ℕ}, 0——k ≃ -1 * coe k
⊢ Negative (n——m) → n < m

case mpr
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
neg_diff : ∀ {k : ℕ}, 0——k ≃ -1 * coe k
⊢ n < m → Negative (n——m)