∀ x. disj(x, rev(y0)) ↔ disj(x, y0) ⊦ disj(x, rev(a + y0)) ↔ disj(x, a + y0)
Used simplifier rules: rev-e: ⊦ rev([]) = [];%list freely generated by [], +;;% ⊦ disj(x, []); (s)