| ⊦ (∃ x. path(r ' + x, H) ∧ (r ' + x).last = r0) ↔ r ≠ null ∧ r ∈ H ∧ (∃ n. reachable-n(H, n, r, r0)) |
∃ x. path(r ' + x, H) ∧ (r ' + x).last = r0 ⊦ r ≠ null ∧ r ∈ H ∧ (∃ n. reachable-n(H, n, r, r0))
r ≠ null ∧ r ∈ H ∧ (∃ n. reachable-n(H, n, r, r0)) ⊦ ∃ x. path(r ' + x, H) ∧ (r ' + x).last = r0