 Notwithstanding the historical and conceptual centrality of the CA described in this section, many important developments in the field could not be presented in the space allowed for this entry. One can relax some of the assumptions in the general characterization of CA provided in  Section 2.1  and get interesting results. The transition rule can be probabilistic and take into consideration more than just one time step (see Richards, Meyer, &amp; Packard 1990: probabilistic automata are widely used to represent the stochastic dynamics of microphysical systems); the cell state updating can be asynchronous (see Ingerson &amp; Buvel 1984); the lattice can be made of non-homogeneous cells following different transition rules (see Kauffman 1984); even the discreteness constraint can be relaxed by having the set of states be the set of real numbers (see Wolfram 2002: 155–157).