摘要：Consider a random permutation drawn from the set of permutations of length n that avoid a given set of one or several patterns of length 3. We show that the number of occurrences of another pattern has a limit distribution, after suitable scaling. In several cases, the limit is normal, as it is in the case of unrestricted random permutations; in other cases the limit is a non-normal distribution, depending on the studied pattern. In the case when a single pattern of length 3 is forbidden, the limit distributions can be expressed in terms of a Brownian excursion.
The analysis is made case by case; unfortunately, no general method is known, and no general pattern emerges from the results.
关键词：Random permutations; patterns; forbidden patterns; limit in distribution; U-statistics
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