of the *finite-range* EPI with high-frequency optical phonons. The effect appears since the finite-range Fröhlich interaction combined with the long-range Coulomb repulsion provides an effective interaction with a deep attraction minimum for two holes on the neighbouring sites, and repulsive for other hole configurations. Bipolarons which are both light and small give rise to Ogg-Schafroth’s bose-condensed state of charged bosons at high-temperatures, since the Bose-Einstein condensate has transition temperature that is inversely proportional to mass. Our conclusion is backed up by analytical [@ale5; @alekor2] and CTQMC studies [@jim2; @jim3]. These studies let us believe that the following recipes is worth investigating to look for room-temperature superconductivity [@jim2]: (a) The parent compound should be an ionic insulator with light ions to form high-frequency optical phonons, (b) The structure should be quasi two-dimensional to ensure poor screening of high-frequency phonons polarized perpendicular to the conducting planes, (c) A triangular lattice is required in combination with strong, on-site Coulomb repulsion to form the small superlight crab bipolaron, (d) Moderate carrier densities are required to keep the system of small bipolarons close to the dilute regime. Clearly most of these conditions are already met in the cuprate superconductors.

Acknowledgements
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I would like to 