| r ∈ H, legal(H), reachable-n(H, n, r, r0) ⊦ r = null, ¬ reachable-n(H, n + 1, r, H[r0] .nxt) ↔ H[r0] .nxt = null |
⊦ reachable-n(H, n + 1, r, r0) ↔ (∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0))
r ∈ H, legal(H), reachable-n(H, n, r, r0) ⊦ r = null, ¬ (∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, H[r0] .nxt)) ↔ H[r0] .nxt = null
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (H[r0] .nxt, r, n, H)]]