| (r ' + x1)[m] = x2 .last, (r ' + x1)[# x2] = x2 .last, path(r ' + x2, H), reachable-n(H, # x2, r, x2 .last), # x2 < m, # x2 < # x1, m ≤ # x1, path(r ' + x1, H) ⊦ x1 = [], x2 = [], ∃ x. path(x, H) ∧ hd x = r ∧ x .last = x2 .last ∧ # x = m + 1 |
(r ' + x1)[m] = x2 .last, (r ' + x1)[# x2] = x2 .last, path(r ' + x2, H), reachable-n(H, # x2, r, x2 .last), # x2 < m, # x2 < # x1, m ≤ # x1, path(r ' + x1, H) ⊦ x1 = [], x2 = [], path(firstn(m + 1, r ' + x1), H) ∧ hd firstn(m + 1, r ' + x1) = r ∧ firstn(m + 1, r ' + x1) .last = x2 .last ∧ # firstn(m + 1, r ' + x1) = m + 1
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (firstn(m + 1, r ' + x1))]]