1. F. Iachello and A. Arima, The Interacting Boson Model (Cambridge Univ. Press, New York, 1987), and references therein.
2. A. Arima, T. Otsuka, F. Lachello and I. Talmi, Phys. Lett. 66B (1977) 205.
3. T. Otsuka, A. Arima, F. Lachello and I. Talmi, Phys. Lett. 76B (1978) 139.
4. T. Otsuka, A. Arima and F. Iachello, Nucl. Phys. A309 (1978) 1.
5. T. Otsuka, Algebraic Approaches to Nuclear Structure: Interacting Boson and Fermion Models, edited by R.F. Casten, (Gordon and Breach, New York, 1993), Chapter 4.