| reach(source, a, n0), b ∈ succ(a) ⊦ succ(a) = ∅, # succ(a) = 0, ∃ m. m < n0 + 2 ∧ reach(source, b, m) |
reach(source, a, n0), b ∈ succ(a) ⊦ succ(a) = ∅, # succ(a) = 0, n0 + 1 < n0 + 2 ∧ reach(source, b, n0 + 1)
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (n0 + 1)]]