  This paper gives methods for understanding invariants of symplectic
quotients. The symplectic quotients considered here are compact symplectic
manifolds (or more generally orbifolds), which arise as the symplectic
quotients of a symplectic manifold by a compact torus. (A companion paper
examines symplectic quotients by a nonabelian group, showing how to reduce to
the maximal torus.)
  Let X be a symplectic manifold, with a Hamiltonian action of a compact torus
T. The main topological result of this paper describes an explicit cobordism
that exists between a symplectic quotient of X by T, and a collection of
iterated projective bundles over components of the set of T-fixed-points.
  The characteristic classes of these bundles can be determined explicitly, and
another result uses this to give formulae for integrals of cohomology classes
over the symplectic quotient, in terms of data localized at the T-fixed points
of X.
