G. Bergman. (2016)cite arxiv:1602.00034Comment: Comments: 50 pages. Main change from version 2: Lemma 26 strengthened to include contractibility statement which in previous version was noted as "likely" in paragraph following that result. Several small typoes also corrected.
M. Pennings, D. Swierstra, и H. Vogt. Proceedings of the 4th International Symposium of Programming Language
Implementation and Logic Programming, Leuven, BE: PLILP '92, стр. 130--144. Berlin, DE, Springer-Verlag, (1992)