Ian Stewart (1) is the professor of mathematics Ian N Stewart (b. 1945-), and co-author of books with Jack Cohen. He is also the author of Wheelers and Heaven. Ian Stewart ,
(2) b. 1928- and Ian Stewart,
(3) b. 1966- are both journalists. Although they appear as one author on the website of publishers Allen & Unwin, their biographical details reveal them to be different people.
(4) Stewart, Ian, 1940- wrote Ta Today: A New Introduction to Transactional Analysis.
(6) is Ian G. McM Stewart