have : Positive b := ‹AP (Positive b)›.ev
ℕ : Type
inst✝¹ : Natural ℕ
ℤ : Type
inst✝ : Integer ℤ
a b : ℤ
denominator_positive✝¹ : AP (Positive b)
c d : ℤ
denominator_positive✝ : AP (Positive d)
x✝ : a//b ≃ c//d
this : a * d ≃ c * b
⊢ sgn (a//b) ≃ sgn (c//d)
ℕ : Type
inst✝¹ : Natural ℕ
ℤ : Type
inst✝ : Integer ℤ
a b : ℤ
denominator_positive✝¹ : AP (Positive b)
c d : ℤ
denominator_positive✝ : AP (Positive d)
x✝ : a//b ≃ c//d
this✝ : a * d ≃ c * b
this : Positive b
⊢ sgn (a//b) ≃ sgn (c//d)