 This was a common error message in the Apple II's BASIC programming language, and the logical step for users of the time would be to review the erroneous line of code with the command "List ###" (again substituting the specific number in question).Typing the secret three-digit code at any time resulted in the game being lost, however, and that included typing such a BASIC command since, unknown to the player, the game was actually still running.Ironically, being able to list the program's code from within it was one way to solve and win the game by means of analyzing the program and deducing a solution.