| m ≠ n0 + 1, lf(0) = a ', m < n0, ∀ n, a. nextl(n, a) ≠ [], ∀ m. m < n0 → lf(m + 1) = nextl(m, lf(m).last) ∧ lf(m) ≠ [] ⊦ lf(m + 1) = nextl(m, lf(m).last), m = n0, n0 = 0 |
lf(0) = a ', m < n0, ∀ n, a. nextl(n, a) ≠ [], ∀ m. m < n0 → lf(m + 1) = nextl(m, lf(m).last) ∧ lf(m) ≠ [] ⊦ lf(m + 1) = nextl(m, lf(m).last), m = n0, n0 = 0, m = n0 + 1