have : n < m := Natural.compare_lt.mp this
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : (n——m).sgn ≃ -1
this✝¹ : ord_sgn (compare n m) ≃ -1
this✝ : ord_sgn (compare n m) ≃ ord_sgn Ordering.lt
this : compare n m = Ordering.lt
⊢ Negative (n——m)
ℕ : Type
inst✝ : Natural ℕ
n m : ℕ
x✝ : (n——m).sgn ≃ -1
this✝² : ord_sgn (compare n m) ≃ -1
this✝¹ : ord_sgn (compare n m) ≃ ord_sgn Ordering.lt
this✝ : compare n m = Ordering.lt
this : n < m
⊢ Negative (n——m)