| legal(H), r ∈ H, legal(H) ∧ r ∈ H → r = null ∨ (∃ r0. reachable(r, r0, H) ∧ H[r0] .nxt = null) ∨ (∃ r0. reachable-n(H, n0, r, r0)) ⊦ r = null, ∃ r0. reachable(r, r0, H) ∧ H[r0] .nxt = null, ∃ r0. reachable-n(H, n0 + 1, r, r0) |
legal(H), r ∈ H, reachable-n(H, n0, r, r0) ⊦ r = null, ∃ r0. reachable(r, r0, H) ∧ H[r0] .nxt = null, ∃ r0. reachable-n(H, n0 + 1, r, r0)
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