Untitled

946
Packard and Wolfram
36. P. Kramer, Non-periodic central space filling with icosahedral symmetry using copies of
seven elementary cells, Acta Crystallogr. A38:257 (1982).
37. M. Garey and D. Johnson, Computers and Intractability: A Guide to the Theory 0/
NP-completeness (Freeman, San Francisco, 1979), p. 257.
38. J. Milnor, Entropy of cellular automaton-maps, Institute for Advanced Study preprint
(May 1984).
39. 1. Milnor, Directional entropies in higher dimensions, rough notes (September 1984).
40. N. Packard, Complexity of growing patterns in cellular automata, Institute for Advanced
Study preprint (October 1983).
41. J. Milnor, Notes on surjective cellular automaton-maps, Institute for Advanced Study
preprint (June 1984).
42. N. D. Mermin, The topological theory of defects in ordered media, Rev. Mod. Phys.
51 :591 (1979).
43. A. Winfree and E. Winfree, Organizing centers in a cellular excitable medium, Purdue
University preprint (July 1984) and Physica D (to be published).