have : Nonzero a := nonzero_iff_pos_or_neg.mpr (Or.inr ‹Negative a›)
ℕ : Type
inst✝⁵ : Natural ℕ
ℤ : Type
inst✝⁴ : Core ℤ
inst✝³ : Addition ℤ
inst✝² : Multiplication ℤ
inst✝¹ : Negation ℤ
inst✝ : Sign ℤ
a : ℤ
tri : AA.ExactlyOneOfThree (a ≃ 0) (Positive a) (Negative a)
c✝ : Negative a
⊢ a ≃ 0 ∨ Nonzero a
ℕ : Type
inst✝⁵ : Natural ℕ
ℤ : Type
inst✝⁴ : Core ℤ
inst✝³ : Addition ℤ
inst✝² : Multiplication ℤ
inst✝¹ : Negation ℤ
inst✝ : Sign ℤ
a : ℤ
tri : AA.ExactlyOneOfThree (a ≃ 0) (Positive a) (Negative a)
c✝ : Negative a
this : Nonzero a
⊢ a ≃ 0 ∨ Nonzero a