| i < 0 ⊦ i0 < 0, gcd(abs(i), abs(i0 + i)) = gcd(i0 + i, i0), 0 < i ∧ i < i0 + i |
abs(i) < i0, i < 0 ⊦ i0 < 0, gcd(abs(i), abs(i0 + i)) = gcd(i0 + i, i0), 0 < i ∧ i < i0 + i
i < 0 ⊦ abs(i) < i0, i0 < 0, gcd(abs(i), abs(i0 + i)) = gcd(i0 + i, i0), 0 < i ∧ i < i0 + i
Used formulas: abs(i) < i0