added tag (characteristic p)
obstruction to smooth lifting of smooth schemes
According to general theory, for a square zero thickening defined by an ideal I: SpecA -> SpecA', there is an obstruction of lifting a smooth scheme X over A to a smooth scheme over A' living in H^2(X,T_X \otimes I).
Can anyone give an example of being obstructed? e.g. a smooth scheme over F_p which does not lift smoothly to Z/(p^2)?