The reducts of equality up to primitive positive interdefinability
arXiv:0810.2270
Abstract
We initiate the study of reducts of relational structures up to primitive positive interdefinability: After providing the tools for such a study, we apply these tools in order to obtain a classification of the reducts of the logic of equality. It turns out that there exists a continuum of such reducts. Equivalently, expressed in the language of universal algebra, we classify those locally closed clones over a countable domain which contain all permutations of the domain.
arXiv comment41 pages; version 3 has been been checked also by non-authors