Leon Horsten is a philosophical logician and philosopher of mathematics, working at the University of Bristol since 2007. His research is concentrated chiefly on bringing formal methods to bear on philosophical problems in the philosophy of science, the philosophy of mathematics, the philosophy of language, epistemology and metaphysics. Formal methods are meant to include not only logical methods, but also methods from other areas of mathematics and computer science (graph theory, probability theory, complexity theory, ...).
Philip Welch is a set theorist and mathematical logician, working in Bristol since 1986. For the period 1997-2000 he was at Kobe University Graduate School setting up a research group in Set Theory. He is the author of some 75 papers in set theory, logic, theories of truth, and transfinite models of computation. He is a subject Co-editor for the Stanford Encyclopaedia of Philosophy for philosophy of mathematics, and is an Editor for set theory of the Journal of Symbolic Logic. His doctoral `grandfather' is Alan Turing, his supervisor at Oxford (1975-78) Robin Gandy, being Turing's only PhD student.