# x + # y ≤ 1 ⊦ x = [], x.rest = [] ∧ y = []
Used simplifier rules: lf-01: ⊦ # x = 1 ↔ x = x.first + [];%fr-07: ⊦ x ≠ [] → (x = x.first + y ↔ x.rest = y);