@inproceedings{STOC-1976-CardozaLM,
	author        = "E. Cardoza and Richard J. Lipton and Albert R. Meyer",
	booktitle     = "{Proceedings of the Eighth Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800113.803630",
	pages         = "50--54",
	publisher     = "{ACM}",
	title         = "{Exponential Space Complete Problems for Petri Nets and Commutative Semigroups: Preliminary Report}",
	year          = 1976,
}