@inproceedings{CAAP-1991-KasangianV,
	author        = "Stefano Kasangian and Sebastiano Vigna",
	booktitle     = "{Proceedings of the Fourth International Joint Conference on Theory and Practice of Software Development, Volume 1: Colloquium on Trees in Algebra and Programming}",
	doi           = "10.1007/3-540-53982-4_13",
	isbn          = "3-540-53982-4",
	pages         = "215--240",
	publisher     = "{Springer}",
	title         = "{Introducing a Calculus of Trees}",
	year          = 1991,
}