| ∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0), ∃ r1. reachable-n(H, n, r, r1) ∧ reachable-n(H, n + 1 - n, r1, r0) ⊦ reachable-n(H, n + 1, r, r0) |
reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0), ∃ r1. reachable-n(H, n, r, r1) ∧ reachable-n(H, n + 1 - n, r1, r0) ⊦ reachable-n(H, n + 1, r, r0)