  The existence of more than one solution for s-wave pairing in the extended
Hubbard model is not often realized. This possibility was noted by Friedberg et
al. [Phys. Rev B50, 10190 (1994)] in the case of two electrons on a lattice,
without further analysis. In the present paper, the second solution is found
also in the case of superconductivity of extended s-wave symmetry in the
extended Hubbard model. The properties of both s-wave solutions are examined by
mean-field methods and thresholds for their appearance are given. A possibility
of the first-order transition is discovered and modifications of the phase
diagram are calculated. Results of this paper in the limit of low electron
density are also applicable to the bound, two-electron pairs.
