∀ a, x0. x1 \ (a ' + x0) = x1 \ x0 ∨ a ∈ x1 ⊦ (a0 + x1) \ (a ' + x0) = (a0 + x1) \ x0, a ∈ a0 + x1
Used simplifier rules: diff-e: ⊦ [] \ y = [];%list freely generated by [], +;;