Algebraic solutions for two-level pairing model in IBM-2 and IVBM A. Jalili-Majarshin, M. A. Jafarizadeh and N. Fouladi Eur. Phys. J. Plus, 131 9 (2016) 337 Published online: 27 September 2016 DOI: 10.1140/epjp/i2016-16337-6