Relatively good results were obtained as long as the strategies tending to deceive came in contact with the strategies that tended to cooperate, thus allowing to be used. Consequently, at the next generation, there is a tendency that the ca cooperative strategies be increasingly rare, being replaced by deceiving ones and thus the very foundation of success is annulled.If two cooperative strategies meet, the results are better than if two deceiving strategies met. Consequently, a minority of cooperative strategies, tit-for-tat, is, thus present in a majority of deceiving strategies. They are called evolutionary stable strategies, because they are established through generations and withstand the invasions of other strategies.In 2004 the strategy tit-for-tat was replaced by the master-and-servant strategy, proposed by the Southampton University, according to which, following a face-to-face meeting and an initial exchange, two roles are used, the exploiter and the victim. Thus the exploiter obtains a leading position. In an incipient population the master-and-servant strategy cannot be established, because the communication between players is coded, concerning their initial behaviour, which could lead to the fact that this strategy breaks the rules of the game.The cooperative strategies can be spread if several conditions are met, such as: several rounds are played, the players can recognize one another from one round to the next, so that, if it is necessary, they can be rewarded and so that they don’t know which is the last round.In the case pf the prisoner’s dilemma played in several rounds various strategies can be used, among which we mention: tit-for-tat, mistrust, spite, master-and-servant or Southampton Strategy, always defect, always cooperate.
The tit-for-tat strategy is mainly open to cooperation, but compensation is used in case of betrayal. Thus, at the first round, cooperation is used, and in the next round the previous move of the game partner is imitated.
The mistrust strategy implies betrayal in the first round, and in the next rounds the previous move of the game partner is imitated. Unlike the tit-for-tat strategy, it is not open for cooperation.
The spite strategy is characterised by cooperation up to the moment when the game partner betrays first, and he will subsequently betray continuously.
According to the master-and-servant strategy, during the first five to ten rounds a coded behaviour is played. The game partner can become an exploiter (the party who always betrays), and the other becomes an exception (the party who cooperates unconditionally). If the game partner does not comply with this strategy, then he betrays, to the detriment of the combatants who take part into the competition.
With the always defect strategy, the player always betrays, without taking into account what the dame partner does, and with the always cooperate strategy, he always cooperates and does not take into account the game partner’s attitude.
3. Three examples of practical application of the “prisoner’s dilemma”
I. We assume the case where two companies A and B extract gold from a gold deposit. For the extraction, the two companies must choose either a polluting technology, or an ecologic technology.
If both companies use a polluting technology, than the profit of each is 2,000,000
m. u. If company A uses an ecologic technology, and company B a polluting technology, then company A obtains a profit of 500,000 m. u., and company B a profit of 2,500,000 m.
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