Since 2002 I have studied the interplay of computability and randomness. For an overview of work up to 2010 see Interactions of Computability and Randomness, Proceedings of the International Congress of Mathematicians, 2010. For recent work see e.g. Coherent randomness tests and computing the K-trivial sets. With L. Bienvenu, N. Greenberg, A. Kucera, and D. Turetsky. J. European Math. Society 18 (2016), 773-812.
My recent interests include the connection of randomness to analysis, ergodic theory, set theory (cardinal characteristics), and reverse mathematics.
I also work on invariant descriptive set theory, in particular for Polish metric spaces.
I apply logical methods to algebraic structures, especially to groups. A recent paper in this direction:
Describing finite groups by short first-order sentences. With Katrin Tent. Israel J. Mathematics, to appear.
I haved studied structures that can be described
by automata, or via Borel relations.
See my survey papers: Describing Groups. Bull. Symb. Logic. 13 no 3 (2007), 305-339
Borel Structures: a brief survey   (with A. Montalban, 2010). Effective Mathematics of the Uncountable, Lecture Notes in Logic 41 (2013), 124-134.
My book ''Computability and Randomness'' was published by Oxford University Press Jan 29, 2009. The revised paperback version was published March 2012.
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Randomness and computability: Open questions. Version of June 30, 2007 with list of results obtained so far.
Published in Bull. Symb. Logic. 12 no 3 (2006) 390-410.
Joint with Joe Miller.