| i = head(depths(t, i + 1)), i ∈ depths(t, i + 1) ⊦ depths(t, i + 1) + depths(t0, i + 1) = [] |
⊦ depths(t, i) ≠ []
depths(t, i + 1) = d + y ∧ depths(t, i + 1) ≠ [], i = d, i ∈ depths(t, i + 1) ⊦ depths(t, i + 1) + depths(t0, i + 1) = []
[[CONCRETESIMPRULES : ([CSIMPELIM : x ≠ [] ⊦ d = head(x) ∧ y = pop(x) ↔ x = d + y])], [EXTRATERMS : (depths(t, i + 1), d, y)]]