  We present universal relations for a two-dimensional Fermi gas with pairwise
contact interactions. The derivation of these relations is made possible by
obtaining the explicit form of a generalized function -- selector -- in the
momentum representation. The selector implements the short-distance boundary
condition between two fermions in a straightforward manner, and leads to simple
derivations of the universal relations, in the spirit of Tan's original method
for the three-dimensional gas.
