| t1 = Node(t, t0), i ' + x = depths(t1, i) + y, i ∈ depths(t1, i) ⊦ x = y ∧ Leaf = t1 |
⊦ depths(Node(t0, t1), i) = depths(t0, i + 1) + depths(t1, i + 1)
⊦ depths(t, i) + x = d ' + y → d ∈ depths(t, i)
i ' + x = (depths(t, i + 1) + depths(t0, i + 1)) + y, i ∈ depths(t, i + 1) ⊦
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ d ∈ x → d ∈ x + y], [CSIMPFORWARD : ⊦ d ' + x = y → d ∈ y], [CSIMPSEQ : ⊦ Leaf ≠ Node(t, t0)], [CSIMPSEQ : ⊦ (x + y) + z = x + y + z], [CSIMPSEQ : ⊦ d ∈ x + y ↔ ¬ ¬ (d ∈ x ∨ d ∈ y)], [CSIMPSEQ : ⊦ i + j = j + i])]]