@MISC{MPB:PN1987:modal,
AUTHOR = "Maria Paola Bonacina",
TITLE = "{P}etri nets for knowledge representation",
HOWPUBLISHED = "Petri Nets Newsletter, No. 27, pages 28--36",
NOTE = "Gesellschaft f{\"u}r Informatik,
special interest group on Petri nets and related system models",
MONTH = "August",
YEAR = 1987}