| legal(H), r ∈ H, reachable-n(H, n0, r, r0) ⊦ r = null, reachable-1(H, r0, H[r0] .nxt), ∃ r0. reachable(r, r0, H) ∧ H[r0] .nxt = null |
⊦ reachable-1(H, r, r0) ↔ r ≠ null ∧ r0 ≠ null ∧ r ∈ H ∧ r0 ∈ H ∧ H[r] .nxt = r0
legal(H), r ∈ H, reachable-n(H, n0, r, r0) ⊦ r = null, r0 ≠ null ∧ H[r0] .nxt ≠ null ∧ r0 ∈ H ∧ H[r0] .nxt ∈ H ∧ H[r0] .nxt = H[r0] .nxt, ∃ r0. reachable(r, r0, H) ∧ H[r0] .nxt = null
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (H[r0] .nxt, r0, H)]]