| perm(x + a ' + x0, y), perm(y, x + a ' + x0) ⊦ a ∈ y |
⊦ a ∈ y ∧ ¬ a ∈ x → ¬ perm(x, y)
Used simplifier rules: ⊦ a ∈ x + y ↔ a ∈ x ∨ a ∈ y; (s)% ⊦ a ∈ b ' ↔ a = b; (s)%a: ⊦ (x + y) + z = x + y + z; from specification list Used terms: a, x + a ' + x0, y