This applet explores the domain of the example 3D cellular automaton Fredkin discussed. It starts by displaying a single cell. Then it activates those cells in the domain - when considering any currently-active cells as the co-domain. This process is then iterated. The result is a display of those cells in the domain of a compound automata, consisting of the concatenation of several consecutive timesteps of the original one. Drag to rotate. Select the "Set" checkbox to toggle individual cells on and off. An essay is available that references this applet here.