1. Agre, P., 2003, Hierarchy and history in Simon’s “Architecture of complexity,” Journal of Learning Sciences. 12: 413–426.
2. Ahl, V. and Allen, T., 1996, Hierarchy Theory: A Vision, Vocabulary, and Epistemology Columbia University Press, NY.
3. Allen, T. and Starr, T., 1982, Hierarchy: Perspectives for Ecological Complexity, Chicago University Press, Chicago.
4. Anderson, P., 1972, More is different: Broken symmetry and the hierarchical nature of science, Science. 177: 393–396.
5. Batty, M., 2005, Hierarchies in cities and city systems, this volume.