  In the Penrose limit, AdS*S space turns into a Cahen-Wallach (CW) space whose
Killing vectors satisfy a Heisenberg algebra. This algebra is mapped onto the
holographic screen on the boundary of AdS. I show that the Heisenberg algebra
on the boundary of AdS may be obtained directly from the CW space by
appropriately constraining the states defined on it. The transformations
generated by the constraint are similar to gauge transformations. The
``holographic screen'' on the CW space is thus obtained as a ``gauge-fixing''
condition.
