⊦ (m * (m + 1)) / 2 < (n * (n + 1)) / 2 ↔ m < n
(1 * (1 + 1)) / 2 < (n * (n + 1)) / 2 ↔ 1 < n ⊦ (n * (n + 1)) / 2 ≤ n ↔ n < 2
Used terms: 1, n