@INPROCEEDINGS{KlaSch:GraphTypes,
	AUTHOR = {Klarlund, N. and Schwartzbach, M.},
	TITLE = {Graph Types},
	BOOKTITLE = {Proc.\ 20th Symp.\ on Princ. of Prog. Lang.},
	YEAR = {1993},
	PAGES = {196-205},
	ORGANIZATION = {ACM},
}