Used simplifier rules: c: ⊦ a + x = a ' + x;%a: ⊦ (x + y) + z = x + y + z;%c-06: ⊦ a ' + x = b ' + y ↔ a = b ∧ x = y;%neq: ⊦ ¬ a ∈ x → x ≠ y + a ' + z;%list freely generated by [], +;;