## Paper: Extensional PERs (at LICS 1990)

**Peter J. Freyd Philip Mulry Giuseppe Rosolini Dana S. Scott**

### Abstract

A search is conducted for a class of PERs (partial equivalence relations on the natural numbers) such that the resulting full subcategory has the expected properties of any good category of CPOs: it should be a CCC (Cartesian closed category) and every endomorphism should have a canonical fixed point. Moreover the reflection functor (usually called the lifting operation) should yield a good notion of partial map. The following topics are discussed: conventions, partial-map classifiers, ExPERS, ExPERS as domains, reflectivity of strict maps, multicorreflectivity of strict maps, the extensional natural numbers, domain equations, and intrinsic descriptions

### BibTeX

@InProceedings{FreydMulryRosoliniS-ExtensionalPERs, author = {Peter J. Freyd and Philip Mulry and Giuseppe Rosolini and Dana S. Scott}, title = {Extensional PERs}, booktitle = {Proceedings of the Fifth Annual IEEE Symposium on Logic in Computer Science (LICS 1990)}, year = {1990}, month = {June}, pages = {346--354}, location = {Philadelphia, PA, USA}, publisher = {IEEE Computer Society Press} }