  The spin chains originating from large-N conformal gauge theories are of a
special kind: The Hamiltonian is not invariant under the symmetry algebra, it
is rather a part of it. This leads to interesting properties within the
asymptotic Bethe ansatz. Here we study an S-matrix with u(1|1) symmetry which
arises in a long-range spin chain with fundamental spins of su(2|1).
