match this with
| Or.inl (_ : -b < -a) =>
  have : a < b := lt_neg_flip.mpr ‹-b < -a›
  have : a ≤ b := le_iff_lt_or_eqv.mpr (Or.inl this)
  exact this
| Or.inr (_ : -b ≃ -a) =>
  have : a ≃ b := AA.inject (Rel.symm ‹-b ≃ -a›)
  have : a ≤ b := le_iff_lt_or_eqv.mpr (Or.inr this)
  exact this
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
x✝ : -b ≤ -a
this : -b < -a ∨ -b ≃ -a
⊢ a ≤ b
no goals