We will call a ladder a one-dimensional periodic structure, which grows in one direction in a straight horizontal or vertical line. We assume that the CA rule is rotationally symmetric, so that ladders and turns work in all four lattice directions. Two more behaviors follow from these requirements, as shown in Fig.
Ladders can end.
Birth, turns, and blocking. With sequences of turns, we can also delay ladders, or end them by blocking them with themselves. The blocking collision will be our main building block for Boolean circuits. If the presence or absence of a ladder corresponds to a wire being true or false, blocking acts as a logical gate as shown in Fig. 2, with inputs a and b and outputs b and a and not b . The logical effects of a blocking collision.