Chapter 6: Starting from Randomness

Section 2: Four Classes of Behavior

History [of cellular automaton classes]

I discovered the classification scheme for cellular automata described here late in 1983, and announced it in January 1984. Much work has been done by me and others on ways to make the classification scheme precise. The notion that class 4 can be viewed as intermediate between class 2 and class 3 was studied particularly by Christopher Langton, Wentian Li and Norman Packard in 1986 for ordinary cellular automata, by Hyman Hartman in 1985 for probabilistic cellular automata and by Hugues Chaté and Paul Manneville in 1990 for continuous cellular automata.

From Stephen Wolfram: A New Kind of Science [citation]