  We study sets $V$ in the tridisc that are relatively polynomially convex and
have the polynomial extension property. If $V$ is one-dimensional, and is
either algebraic, or has polynomially convex projections, we show that it is a
retract. If $V$ is two-dimensional, we show that either it is a retract, or,
for any choice of the coordinate functions, it is the graph of a function of
two variables.
