| n0 + m ≤ # buf1 ⊦ (∀ n. n0 + # buf0 ≤ n ∧ n < (n0 + # buf0) + m → (buf0 + buf1)[n] = empty) ↔ (∀ n. n0 ≤ n ∧ n < n0 + m → buf1[n] = empty) |
n0 + m ≤ # buf1, ∀ n. n0 + # buf0 ≤ n ∧ n < (n0 + # buf0) + m → (buf0 + buf1)[n] = empty ⊦ ∀ n. n0 ≤ n ∧ n < n0 + m → buf1[n] = empty
n0 + m ≤ # buf1, ∀ n. n0 ≤ n ∧ n < n0 + m → buf1[n] = empty ⊦ ∀ n. n0 + # buf0 ≤ n ∧ n < (n0 + # buf0) + m → (buf0 + buf1)[n] = empty