3 C. Mahulea C. Seatzu M.P. Cabasino L. Recalde M. Silva 2009 Observer Design for Untimed Continuous Petri Nets ACC'09: Proceedings of the 2009 conference on American Control Conference St. Louis, Missouri, USA IEEE Press 06/2009 0743-1619 http%3A%2F%2Fieeexplore.ieee.org%2Fstamp%2Fstamp.jsp%3Ftp%3D%26arnumber%3D5159893%26isnumber%3D5159764