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