H. A. Bethe, 1931, Z. Physik, 71, 205, 10.1007/BF01341708
E. Lieb, 1963, Phys. Rev., 130, 1605, 10.1103/PhysRev.130.1605
J. B. McGuire, 1964, J. Math. Phys., 5, 622, 10.1063/1.1704156
C. N. Yang, 1966, Phys. Rev., 150, 321, 10.1103/PhysRev.150.321
M. Gaudin, 1967, Phys. Letters, 24A, 55, 10.1016/0375-9601(67)90193-4
E. Lieb, 1962, Phys. Rev., 125, 164, 10.1103/PhysRev.125.164
J. B. McGuire, 1965, J. Math. Phys., 6, 432, 10.1063/1.1704291
J. B. McGuire, 1966, J. Math. Phys., 7, 123, 10.1063/1.1704798
M. Flicker, 1967, Phys. Rev., 161, 179, 10.1103/PhysRev.161.179
E. Lieb, 1963, Phys. Rev., 130, 1616, 10.1103/PhysRev.130.1616
C. N. Yang, 1967, Proceedings of Eastern Theoretical Conference, November, 1966, Brown University