⊦ m0 ≤ # buf ∧ m ≠ 0 → (m ≤ datasize(buf, m0) ↔ (∃ n. n + 1 ≥ m ∧ n < m0 ∧ buf[n] ≠ empty))
[Concretesimprules(()), Extraterms((m0bufm))]