Böhm's Theorem, Church's Delta, Numeral Systems, and Ershov Morphisms.

Richard Statman Henk Barendregt Böhm's Theorem, Church's Delta, Numeral Systems, and Ershov Morphisms. 40-54 2005 conf/birthday/2005klop Processes, Terms and Cycles http://dx.doi.org/10.1007/11601548_5 db/conf/birthday/klop2005.html#StatmanB05