  Working in the context of the proposed duality between 3D higher spin gravity
and 2D W_N minimal model CFTs, we compute a class of four-point functions in
the bulk and on the boundary, and demonstrate precise agreement between them.
This is the first computation of a correlator in 3D higher spin gravity whose
functional form is not fixed by conformal invariance. In the bulk we make use
of elegant methods to solve the scalar field equation using only matrix
manipulations, while on the CFT side we employ the Coulomb gas representation.
Comparison is made in the semiclassical limit, in which the central charge is
taken to infinity at fixed N. Along the way, we establish the rules for
computing correlation functions of multi-trace operators in higher spin
gravity. The method involves solving the scalar master field equation in a
general representation of the bulk gauge algebra. Although most of our work is
carried out for the bulk theory based on sl(N) x sl(N), we also discuss how our
methods can be adapted to the hs[\lambda] x hs[\lambda] theory, which is
relevant in the 't Hooft limit.
