arXiv subjects
Publications and source records attributed to Peter Ouwehand.
These notes are concerned with the existence and the basic properties of the set-theoretic universes for nonstandard analysis, compiled by a beginner in the subject. It assumes a basic background in first-order logic, though the necessary material is revised in Appendix A. Needless to say, none of the material presented here is original, but has been adapted from standard sources.
In stochastic analysis, the flow of information through time is typically modelled using a filtration. We introduce some of the basic ideas involving enlargements of filtration. Here, we focus mainly on initial enlargements, where a given filtration is enlarged with knowledge of an additional random variable. This has applications to the modelling of insider trading in mathematical finance.
This is the first draft of a set of lecture notes developed for one-half of a seminar on two approaches to the notion of "Abelian", namely those of universal algebra, and of category theory. The half pertaining to the universal-algebraic perspective is covered here. All material has been adapted from the following sources: 1. Commutator Theory for Congruence Modular Varieties, by Ralph Freese and Ralph McKenzie. 2. Geometrical Methods in Congruence Modular Algebras, by H. Peter Gumm 3. Congruence Modular Varieties: Commutator Theory and Its Uses, by Ralph McKenzie and John Snow
This paper studies absolute retracts in congruence modular varieties of universal algebras. It is shown that every absolute retract with finite dimensional congruence lattice is a product of subdirectly irreducible algebras. Further, every absolute retract in a residually small variety is the product of an abelian algebra and a centerless algebra.