| ∀ i. ¬ min(depths(t0, i)) < i, ∀ i. ¬ min(depths(t1, i)) < i, min(depths(Node(t0, t1), i)) < i ⊦ |
⊦ depths(Node(t0, t1), i) = depths(t0, i + 1) + depths(t1, i + 1)
min(depths(t0, i + 1) + depths(t1, i + 1)) < i, ∀ i. ¬ min(depths(t0, i)) < i, ∀ i. ¬ min(depths(t1, i)) < i ⊦
[[CONCRETESIMPRULES : ()]]