case mp =>
  intro (_ : ¬(p ≤ q))
  show sgn (p - q) ≃ 1
  have : ¬(sgn (p - q) ≄ 1) := mt le_sgn.mpr ‹¬(p ≤ q)›
  have : sgn (p - q) ≃ 1 := Decidable.of_not_not this
  exact this
ℕ ℤ ℚ : Type
inst✝¹⁰ : Natural ℕ
inst✝⁹ : Integer ℤ
inst✝⁸ : Core ℚ
inst✝⁷ : Addition ℚ
inst✝⁶ : Multiplication ℚ
inst✝⁵ : Negation ℚ
inst✝⁴ : Sign ℚ
inst✝³ : Subtraction ℚ
inst✝² : Reciprocation ℚ
inst✝¹ : Division ℚ
inst✝ : Order ℚ
p q : ℚ
⊢ ¬p ≤ q → sgn (p - q) ≃ 1
no goals