This is the standard structure of a program to play a game on a computer. Programs must first require you check the move is legal before any other step, but this is a minor detail. Then there is usually a set of more or less formal rules to be obeyed, followed by some much vaguer rules. Thus a game program has a lot of heuristics in it (heuristic—to invent or discover), moves which are plausible and likely to lead you to a win but are not guaranteed to do so.
