⊦ n < # x ∧ ixs = pushx(n, ixs0, x) → ixs = ixs0 + n ' ' ∨ (∃ m. m < # ixs0 ∧ ixs = ixs0[m, n + ixs0[m]])
[Concretesimprules(()), Extraterms((nxpushx(n, ixs, x)ixs))]