  We develop a method of singularity analysis for conformal graphs which, in
particular, is applicable to the holographic image of AdS supergravity theory.
It can be used to determine the critical exponents for any such graph in a
given channel. These exponents determine the towers of conformal blocks that
are exchanged in this channel. We analyze the scalar AdS box graph and show
that it has the same critical exponents as the corresponding CFT box graph.
Thus pairs of external fields couple to the same exchanged conformal blocks in
both theories. This is looked upon as a general structural argument supporting
the Maldacena hypothesis.
