A general analytical solution for the variance-to-mean Feynman-alpha formulas for a two-group two-point, a two-group one-point and a one-group two-point casesDina Chernikova, Wang Ziguan, Imre Pázsit and Lénárd PálEur. Phys. J. Plus, 129 11 (2014) 259DOI: https://doi.org/10.1140/epjp/i2014-14259-y