Overall, however, Whitehead's influence is very difficult to characterize. In English-speaking countries, his primary works are little-studied outside of Claremont and a select number of liberal graduate-level theology and philosophy programs. Outside of these circles his influence is relatively small and diffuse, and has tended to come chiefly through the work of his students and admirers rather than Whitehead himself. For instance, Whitehead was a teacher and long-time friend and collaborator of Bertrand Russell, and he also taught and supervised the dissertation of Willard Van Orman Quine, both of whom are important figures in analytic philosophy – the dominant strain of philosophy in English-speaking countries in the 20th century. Whitehead has also had high-profile admirers in the continental tradition, such as French post-structuralist philosopher Gilles Deleuze, who once dryly remarked of Whitehead that "he stands provisionally as the last great Anglo-American philosopher before Wittgenstein's disciples spread their misty confusion, sufficiency, and terror." French sociologist and anthropologist Bruno Latour even went so far as to call Whitehead "the greatest philosopher of the 20th century."