1. Rabin's Proof of the Undecidability of the Reachability Set Inclusion Problem of Vector Addition Systems;Baker,1973
2. Computational Complexity of the Word Problem for Commutative Semigroups;Cardoza,1975
3. The Mathematical Theory of Context Free Languages;Ginsburg,1966
4. The Equality Problem for Vector Addition Systems is Undecidable;Hack,1975
5. Decision Problems for Petri Nets and Vector Addition Systems;Hack,1975