Proof step 47 from proof nextl-lemma-butlast-nonempty (previous step)
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 + 1, m = n0
Heuristic quantifier closing applied rule all left