  Contrary to popular belief, asymptotically anti-de Sitter solutions of
gravitational theories cannot be obtained by taking initial data (satisfying
the constraints) on a spacelike surface, and choosing an arbitrary conformal
metric on the timelike boundary at infinity. There are an infinite number of
corner conditions that also must be satisfied where the initial data surface
hits the boundary. These are well known to mathematical relativists, but to
make them more widely known we give a simple explanation of why these
conditions exist and discuss some of their consequences. An example is given
which illustrates their power. Some implications for holography are also
mentioned.
