  The Hall coefficient data for cuprates show that number of carriers exceeds
external doping $x$ at higher $x$ and varies with temperature. Hence, spins on
the Cu-sites are not conserved. Activation energy for thermally excited
carriers equals the energy between the Fermi surface "arc" and the band bottom
near the van Hove singularities. Crossover from marginal Fermi liquid- to
pseudogap- regime happens at temperatures at which number of activated carriers
gets comparable with the number of externally doped holes. Implications for the
$(T,x)$-phase diagram of cuprates are discussed.
