n = n0 + m, m ≤ n ⊦ (σ to n) + σ0 from m = ((σ from m) to n0) + σ0, # σ < ⌜n⌝
Used simplifier rules: n ≤ m ⊦ n0 = m - n ↔ m = n0 + n; (elim) Used terms: n, m, n0