@article{ZNSL_2016_448_a6,
     author = {V. Gerdt and A. Khvedelidze and Yu. Palii},
     title = {On the ring of local unitary invariants for mixed $X$-states of two qubits},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {107--123},
     publisher = {mathdoc},
     volume = {448},
     year = {2016},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2016_448_a6/}
}