case mpr =>
  intro (_ : -b < -a)
  show a < b
  have : Positive (-a - -b) := gt_iff_pos_diff.mp ‹-b < -a›
  apply gt_iff_pos_diff.mpr
  show Positive (b - a)
  exact AA.substFn ‹-a - -b ≃ b - a› ‹Positive (-a - -b)›
ℕ : Type
inst✝⁷ : Natural ℕ
ℤ : Type
inst✝⁶ : Core ℤ
inst✝⁵ : Addition ℤ
inst✝⁴ : Multiplication ℤ
inst✝³ : Negation ℤ
inst✝² : Subtraction ℤ
inst✝¹ : Sign ℤ
inst✝ : Order ℤ
a b : ℤ
this : -a - -b ≃ b - a
⊢ -b < -a → a < b
no goals