ABSTRACT
The transition from wide -band electrons (or large polarons) to small polarons is extremely sharp as discussed in Chapter 4. Nevertheless the evolution from the Fermi liquid to the charged Bose liquid might vary smoothly with the polaronic BCS -like superconductivity in a very narrow region of the coupling constant. The latter has high Tc due to the large density of states in the extremely narrow (less than lO3^ ) polaronic band. Therefore we first consider the polaronic superconductivity, which is realised if the Coulomb repulsion almost compensates the attraction.
