case mp =>
  intro (_ : -p ≃ 0)
  show p ≃ 0
  calc
    p      ≃ _ := eqv_symm add_identR
    p + 0  ≃ _ := add_substR (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