| a ∈ y ⊦ perm(x + a ' + x0, y) ↔ perm(x + x0, y -1l a) |
∀ a, y, x0. a ∈ y → (perm(x1 + a ' + x0, y) ↔ perm(x1 + x0, y -1l a)), a ∈ y ⊦ perm((a0 + x1) + a ' + x0, y) ↔ perm((a0 + x1) + x0, y -1l a)
Used simplifier rules: del-01: ⊦ perm(a ' + x, y) ↔ ¬ ¬(a ∈ y ∧ perm(x, y -1l a));%perm-l: ⊦ perm(a ' + x, y) ↔ a ∈ y ∧ perm(x, y -1l a);%list freely generated by [], +;;%Nil: ⊦ [] + x = x; from specification list%a: ⊦ (x + y) + z = x + y + z; from specification list