case mpr =>
  intro (_ : p ≃ 0)
  show -p ≃ 0
  calc
    -p     ≃ _ := eqv_symm add_identL
    0 + -p ≃ _ := add_substL (eqv_symm ‹p ≃ 0›)
    p + -p ≃ _ := add_inverseR
    0      ≃ _ := eqv_refl
ℕ ℤ : Type
inst✝⁶ : Natural ℕ
inst✝⁵ : Integer ℤ
ℚ : Type
inst✝⁴ : Core ℚ
inst✝³ : Addition ℚ
inst✝² : Multiplication ℚ
inst✝¹ : Negation ℚ
inst✝ : Subtraction ℚ
p : ℚ
⊢ p ≃ 0 → -p ≃ 0
no goals