  From the 1980s to the present, category theory has found new applications. In theoretical computer science, category theory is now firmly rooted, and contributes, among other things, to the development of new logical systems and to the semantics of programming. (Pitts 2000, Plotkin 2000, Scott 2000, and the references therein). Its applications to mathematics are becoming more diverse, even touching on theoretical physics, which employs higher-dimensional category theory — which is to category theory what higher-dimensional geometry is to plane geometry — to study the so-called “quantum groups” and quantum field theory (Majid 1995, Baez &amp; Dolan 2001 and other publications by these authors).