have : Negative (m——n) := neg_diff_lt.mpr ‹m < n›
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : m < n
⊢ NonzeroWithSign (n——m) 1
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : m < n
this : Negative (m——n)
⊢ NonzeroWithSign (n——m) 1