© 2004 by Oxford University Press
An additive measure in o-minimal expansions of fields

1 Dipartimento di Matematica, Università di Pisa, Via Buonarroti 2, 56127 Pisa, Italy, 2 Departamento de Matemáticas, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain *
Given an o-minimal structure M which expands a field, we define, for each positive integer d, a real-valued additive measure on a Boolean algebra of subsets of Md and we prove that all the definable sets included in the finite part Fin(Md) of Md are measurable. When the domain of M is R we obtain Lebesgue measure, but restricted to a proper subalgebra of that of the Lebesgue measurable sets (the Jordan measurable sets). Our measure has good logical properties, being invariant under elementary extensions and under expansions of the language. In the final part of the paper we consider the problem of defining an analogue of the Haar measure for definably compact groups.
Received 1 November 2003.
* E-mail: berardu{at}dm.unipi.it
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