0 QTRS
.(1, x) → x .(x, 1) → x .(i(x), x) → 1 .(x, i(x)) → 1 i(1) → 1 i(i(x)) → x .(i(y), .(y, z)) → z .(y, .(i(y), z)) → z .(.(x, y), z) → .(x, .(y, z)) i(.(x, y)) → .(i(y), i(x))