In: Theoretical Computer Science, Vol. 64, No. 3, pages 343-350. May 1989.
Abstract: The inclusion problem for reachability sets of vector addition sytems in general is undecidable, even though the reachability problem itself is known to be decidable. The authors show that any one-dimensional projection of the reachability set of an arbitrary vector additon system is semilinar, and hence ``simple''.