| n < # buf, n < n1, ∀ n1, buf. n ≤ n1 ∧ n ≤ # buf → (datasize(buf, n) = datasize(buf, n1) ↔ (∀ n2. n ≤ n2 ∧ n2 < n1 → buf[n2] = empty)) ⊦ (buf[n] = empty ⊃ datasize(buf, n);n + 1) = datasize(buf, n1) ↔ (∀ n0. n < n0 ∧ n0 < n1 → buf[n0] = empty) |
(buf[n] = empty ⊃ datasize(buf, n);n + 1) = datasize(buf, n1), n < n1, n < # buf, ∀ n1, buf. n ≤ n1 ∧ n ≤ # buf → (datasize(buf, n) = datasize(buf, n1) ↔ (∀ n2. n ≤ n2 ∧ n2 < n1 → buf[n2] = empty)) ⊦ ∀ n0. n < n0 ∧ n0 < n1 → buf[n0] = empty
n < n1, n < # buf, ∀ n1, buf. n ≤ n1 ∧ n ≤ # buf → (datasize(buf, n) = datasize(buf, n1) ↔ (∀ n2. n ≤ n2 ∧ n2 < n1 → buf[n2] = empty)), ∀ n0. n < n0 ∧ n0 < n1 → buf[n0] = empty ⊦ (buf[n] = empty ⊃ datasize(buf, n);n + 1) = datasize(buf, n1)