disj(a ' + x, a0 + y0), disj(x, a0 + y0), a ∈ a0 + y0, ∀ x, a. ¬(disj(x, y0) ∧ disj(a ' + x, y0) ∧ a ∈ y0) ⊦
Used simplifier rules: list freely generated by [], +;;% ⊦ ¬ a ∈ []; (s)