  For the Asymmetric Traveling Salesman Problem (ATSP), it is known that the
Dantzig-Fulkerson-Johnson (DFJ) polytope is contained in the
Miller-Tucker-Zemlin (MTZ) polytope. The analytic proofs of this fact are quite
long. Here, we present a proof which is combinatorial and significantly shorter
by relating the formulation to distances in a modified graph.
