  Recently, exact agreement has been found between bulk and boundary
three-point functions in AdS_3 x S^3 x T^4 with NSNS fluxes. This represents a
non-trivial check of AdS/CFT correspondence beyond the supergravity
approximation as it corresponds to an exact worldsheet computation. When taking
a closer look at this computation, one notices that a crucial point for the
bulk-boundary agreement to hold is an intriguing mutual cancellation between
worldsheet contributions corresponding to the AdS_3 and to the S^3 pieces of
the geometry, what results in a simple factorized form for the final
three-point function. In this note we review this cancellation and clarify some
points about the analytic relation between the SU(2) and the SL(2,R) structure
constants. In particular, we dicuss the connection to the Coulomb gas
representation. We also make some comments on the four-point function.
