calc
  _ ≃ sgn p       := Rel.refl
  _ ≃ sgn (p - 0) := sgn_subst (eqv_symm sub_zero)
  _ ≃ 1           := ‹sgn (p - 0) ≃ 1›
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
x✝ : p > 0
this : sgn (p - 0) ≃ 1
⊢ sgn p ≃ 1
no goals