  We consider an incomplete multi-asset binomial market model. We prove that
for a wide class of contingent claims the extremal multi-step martingale
measure is a power of the corresponding single-step extremal martingale
measure. This allows for closed form formulas for the bounds of a no-arbitrage
contingent claim price interval. We construct a feasible algorithm for
computing those boundaries as well as for the corresponding hedging strategies.
Our results apply, for example, to European basket call and put options and
Asian arithmetic average options.
