| # x = n0 + n, ∀ x0, n0, n. # x0 < # x → # x0 = n0 + n → # butlastn(n, x0) = n0 ⊦ x = [], # butlastn(n, x) = n0 |
⊦ x ≠ [] → (∃ y, a. x = y + a ')
x ≠ [] → (∃ y, a. x = y + a '), # x = n0 + n, ∀ x0, n0, n. # x0 < # x → # x0 = n0 + n → # butlastn(n, x0) = n0 ⊦ x = [], # butlastn(n, x) = n0
Used terms: x