A. M��le, and H. Vogler. Proceedings of the Fuji International Workshop in Functional and
Logic Programming, World Scientific Publishing Co. Pte Ltd., (1995)
J. Engelfriet. 7th Coll. on Trees in Algebra and Programming (CAAP '82), Lille, See also: memorandum 363, Onderafdeling der Informatica, Tech. Hogeschool
Twente (1981)..(March 1982)