  In this paper, we study Hamiltonian R-actions on symplectic orbifolds [M/S],
where R and S are tori. We prove an injectivity theorem and generalize
Tolman-Weitsman's proof of the GKM theorem in this setting. The main example is
the symplectic reduction X//S of a Hamiltonian T-manifold X by a subtorus S of
T. This includes the class of symplectic toric orbifolds. We define the
equivariant Chen-Ruan cohomology ring and use the above results to establish a
combinatorial method of computing this equivariant Chen-Ruan cohomology in
terms of orbifold fixed point data.
