and y are the same as in the MCell notation. Thus, in this notation, Conway's Game of Life is denoted B3/S23. The "B" in this format stands for "birth" and the "S" stands for "survival". A selection of rules There are 218 = 262,144 possible rules, only a small fraction of which have been studied in any detail. In the descriptions below, all rules are specified in Golly/RLE format. Several more rules are listed and described in the MCell rule list and by , including some rules with B0 in which the background of the field of cells alternates between live and dead at each step. Any automaton of the above form that contains the element B1 (e.g. B17/S78, or B145/S34) will always be explosive for any finite pattern: at any step, consider the cell (x,y) that has minimum x-coordinate among cells that are on, and among such cells the one with minimum y-coordinate. Then the cell (x-1,y-1) must have exactly one neighbor, and will become on in the next step. Similarly, the pattern must grow at each step in each of the four diagonal directions. Thus, any nonempty starting pattern leads to explosive growth. Any automaton of the above form that does not include any of B0, B1, B2 or B3 cannot support movement or expansion of patterns because any cell outside a rectangular building box containing the pattern has at most three on neighbours. Most finite patterns in rules whose notation begins with B2, and all finite patterns in rules beginning with B1, grow in all directions rather than remaining of bounded size, with a front that moves at the speed of light. Thus, the remaining "interesting" rules are the ones beginning with B3 (Game of Life, Highlife, Morley, 2x2, Day&Night) or beginning with B0 (and not including S8, as otherwise the dual can be studied instead). Generalizations There are other cellular automata which are inspired by the Game of Life, but which do not fit the definition of "" given in this article, because their neighborhoods are larger than the Moore neighborhood, or they are defined on three-dimensional lattices, or they use a different lattice topology. For example: Non-totalistic rules depend on the configuration of live cells in the neighborhood. Non-isotropic rules that behave differently in different directions. There are 2512≈1.34*10154 rules of this kind, including isotropic rules. Isotropic non-totalistic rules behave identically under rotation and reflection.