Research interests
My main research interests originate in the use of temporal logics in
system verification, but spread to cover many connected areas.
Fixpoint logics
A central area of my research for the last twenty years has been
fixpoint logics, and particularly the modal mucalculus. These provide
a foundational logic for verification using the temporal logic
paradigm, and also have a wealth of intrinsically interesting
mathematical properties.
As a consequence of this interest, I have also become interested in
fixpoints in general, which has led to some forays into (mostly quite
elementary!) descriptive set theory.
True concurrency
A longstanding interest is theories and models of true
concurrency, in which causality and the independence of parallel
components are taken seriously.
Independencefriendly logic
In the last few years, I have been working on modal analogues of Hintikka's
IndependenceFriendly Logic. This was inspired by its intuitively
obvious links with concurrency  an intuition which takes a while to
pin down!
Natural language
I have always been interested in natural language, particularly
phonology, and recently I have started to do a little real
work in the area, something which I hope to continue and deepen.
Papers and preprints
Selected publications:
Here are a few recent and/or popular publications:
 A journal paper on the use of
simulation in phonology.
 The journal paper on the
phonology of clicks in Khoisan.
 A CSL paper with a new game semantics
for dependence logic.
 A poster about the difficulty of
learning complex vowel systems.
 A preprint of a chapter on
mucalculi in the Handbook of Modal Logic.

The journal version of two papers on
fixpoints and parity conditions in descriptive set theory, and a
conference paper dealing with
one of the problems raised there.
 A full version of a paper on fixpoint
extensions of independencefriendly logic, and a full paper on the complexity of such logics.

A paper in a Festschrift for
Gabriel Sandu
considering the use of Henkin quantification in modal logic.
 A preprint of an introduction
to modal mucalculus, appearing as a chapter in the Handbook of
Process Algebra

The journal version of the original paper
establishing the strictness of the modal mucalculus alternation
hierarchy, and a journal version of two conference papers,
simplifying the proof, and addressing the issue of Niwinski's fixpoint
algebras on trees.
Most of my papers and preprints are online,
accompanied by a short description and notes about dependencies.
Slides from talks
My talks page has the slides from some of my
seminar etc. talks. This material will be moved into the publications
page, but is currently separate.