| ∀ i. depths(t0, i) ≠ [], ∀ i. depths(t1, i) ≠ [], depths(Node(t0, t1), i) = [] ⊦ |
⊦ depths(Node(t0, t1), i) = depths(t0, i + 1) + depths(t1, i + 1)
depths(t0, i + 1) = [], depths(t1, i + 1) = [], ∀ i. depths(t0, i) ≠ [], ∀ i. depths(t1, i) ≠ [] ⊦
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ (x + y) + z = x + y + z], [CSIMPSEQ : ⊦ ¬ x + y ≠ [] ↔ x = [] ∧ y = []])]]