Conclusions
1. Warm Dark Matter with mass mX ~ 1 keV can solve
most (but not all?) small-scale problems of CDM.
2. WDM, if too hot, can introduce new problems:
e.g. Lya forest statistics, reionization.
3. Reionization by z=6 requires  mX 1 keV, or
unusually high efficiency of ionizing photon production.