| perm(x1 + a0 ' + x0, y -1l a0), perm(y -1l a0, x1 + a0 ' + x0), a0 ∈ y ⊦ a0 ∈ y -1l a0 |
⊦ 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: a0, x1 + a0 ' + x0, y -1l a0