  Redshift-space distortions (RSD) in galaxy redshift surveys generally break
both the isotropy and homogeneity of galaxy distribution. While the former
aspect is particularly highlighted as a probe of growth of structure induced by
gravity, the latter aspect, often quoted as wide-angle RSD but ignored in most
of the cases, will become important and critical to account for as increasing
the statistical precision in next-generation surveys. However, the impact of
wide-angle RSD has been mostly studied using linear perturbation theory. In
this paper, employing the Zel'dovich approximation, i.e., first-order
Lagrangian perturbation theory for gravitational evolution of matter
fluctuations, we present a quasi-linear treatment of wide-angle RSD, and
compute the cross-correlation function. The present formalism consistently
reproduces linear theory results, and can be easily extended to incorporate
relativistic corrections (e.g., gravitational redshift).
