| ⊦ ((n + 1) * (n + 2)) / 2 < ((m + 1) * (m + 2)) / 2, n < m, m0 ≤ m ∧ m ≤ n → (m * (m + 1)) / 2 + m0 < ((n + 1) * (n + 2)) / 2 |
⊦ ¬ m < n ↔ n ≤ m
⊦ ¬ ((m + 1) * (m + 2)) / 2 ≤ ((n + 1) * (n + 2)) / 2, n < m, m0 ≤ m ∧ m ≤ n → (m * (m + 1)) / 2 + m0 < ((n + 1) * (n + 2)) / 2
Used terms: ((m + 1) * (m + 2)) / 2, ((n + 1) * (n + 2)) / 2