Page 65 of Feynman's Lectures on Computation introduces a problem of message passing. A 1D line of cells can only influence neighbors to each side. One cell is turned on, and all cells must reach an identical "firing" state. The nearest-neighbor character of this problem makes it soluble by means of cellular automata. This Demonstration uses a 7-color rule that would be about in base 10 (see the program for the exact value).