match this with
| Or.inl (_ : a < b) =>
  have : -b < -a := lt_neg_flip.mp ‹a < b›
  have : -b ≤ -a := le_iff_lt_or_eqv.mpr (Or.inl this)
  exact this
| Or.inr (_ : a ≃ b) =>
  have : -b ≃ -a := AA.subst₁ (Rel.symm ‹a ≃ b›)
  have : -b ≤ -a := 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✝ : a ≤ b
this : a < b ∨ a ≃ b
⊢ -b ≤ -a
no goals