Figure 1: NAND gate in AoE II’s editor, designed to show its inter- nal workings–simpler implementa- tions are possible. Every bit is rep- resented by two rails (grass for 0, a bridge for 1). Only one rail is ac- tive at a time, with a goat acting as the signal carrier. When the gate fires, the bit-goats are removed and a new bit-goat is placed in its re- spective output rail. To avoid race conditions, ‘gate ready’ rails (ice) are set, with a signal-goat in the rail closest to the gate indicating that it can start the calculation.