The necessary condition for using the theory of a “trick” is that players are to have insufficient information about each other. In this case the “trick” consists in guessing the intentions of the adversary on condition of hiding one’s own intentions: a positive “trick” and a negative “trick”. The tactics of every player is to be very flexible, and one and the same “trick” should not be used for many times, otherwise it will become “tactics” and will revert, like a boomerang, back to its user. The player should strive to modify his game according to the reaction of his adversary by making the most successful choice for this situation: hence comes the probability of probabilities.

The practical value of the threshold d, for which the alternative of “success” with probability d and death with probability 1 – d is preferred to ”certain defeat”, depends on the boldness of the famous English detective.The game theory finds application also in the economic life for strategic calculations. But the problems that arise in this case are quite difficult…