  We consider the problem of minimizing a convex function over a convex set
given access only to an evaluation oracle for the function and a membership
oracle for the set. We give a simple algorithm which solves this problem with
$\tilde{O}(n^2)$ oracle calls and $\tilde{O}(n^3)$ additional arithmetic
operations. Using this result, we obtain more efficient reductions among the
five basic oracles for convex sets and functions defined by Gr\"otschel, Lovasz
and Schrijver.
