Global actions were introduced by A. Bak to give a combinatorial approach to higher $K$-theory, in which control is kept of the elementary operations through paths and paths of paths. This paper is intended as an introduction to this circle of ideas, including the homotopy theory of global actions, which one obtains naturally from the notion of path of elementary operations. Emphasis is placed on developing examples taken from combinatorial group theory, as well as $K$-theory. The concept of groupoid atlas plays a clarifying role.
Journal of Homotopy and Related Structures, Vol. 1(2006), No. 1, pp. 101-167 http://jhrs.rmi.acnet.ge/volumes/2006/n1a5/