  We construct a two parameter family of 2-particle Hamiltonians closed under
the duality operation of interchanging the (relative) momentum and coordinate.
Both coordinate and momentum dependence are elliptic, and the modulus of the
momentum torus is a non-trivial function of the coordinate. This model contains
as limiting cases the standard Ruijsenaars-Calogero and Toda family of
Hamiltonians, which are at most elliptic in the coordinates, but not in the
momenta.
