  Using a six-orientifold on top of a NS-fivebrane we construct a chiral N=1
supersymmetric gauge theory in four dimensions with gauge group SU(N_c) and
matter in the symmetric, antisymmetric and (anti)fundamental representations.
Anomaly cancellation is fulfilled by the requirement of a smooth RR 7-form
charge distribution and leads us to the introduction of 8 half D-sixbranes
ending on the NS-fivebrane. We obtain the dual model from branes by a linking
number argument. We check explicitly the 't Hooft anomaly matching conditions
and the map between deformations in the original and the dual model.
