  The Aztec diamond of order $n$ is the union of lattice squares in the plane
intersecting the square $|x|+|y|<n$. The Aztec diamond theorem states that the
number of domino tilings of this shape is $2^{n(n+1)/2}$. It was first proved
by Elkies, Kuperberg, Larsen and Propp in 1992. We give a new simple proof of
this theorem.
