  The identities for elliptic gamma functions discovered by A. Varchenko and
one of us are generalized to an infinite set of identities for elliptic gamma
functions associated to pairs of planes in 3-dimensional space. The language of
stacks and gerbes gives a natural framework for a systematic description of
these identities and their domain of validity. A triptic curve is the quotient
of the complex plane by a subgroup of rank three (it is a stack). Our
identities can be summarized by saying that elliptic gamma functions form a
meromorphic section of a hermitian holomorphic abelian gerbe over the universal
oriented triptic curve.
