  Let a polyhedral convex set be given by a finite number of linear
inequalities and consider the problem to project this set onto a subspace. This
problem, called polyhedral projection problem, is shown to be equivalent to
multiple objective linear programming. The number of objectives of the multiple
objective linear program is by one higher than the dimension of the projected
polyhedron. The result implies that an arbitrary vector linear program (with
arbitrary polyhedral ordering cone) can be solved by solving a multiple
objective linear program (i.e. a vector linear program with the standard
ordering cone) with one additional objective space dimension.
