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First Occurrence in Pairs of Long Words: A Penney-ante Conjecture of Pevzner

Published online by Cambridge University Press:  12 September 2008

Dudley Stark
Dudley Stark
Affiliation:
Institut für Angewandte Mathematik, Universität Zürich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland
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Abstract

Suppose X1, X2,… is a sequence of independent and identically distributed random elements whose values are taken in a finite set S of size |S| ≥ 2 with probability distribution ℙ(X = s) = p(s) > 0 for s ∈ S. Pevzner has conjectured that for every probability distribution ℙ there exists an N > 0 such that for every word A with letters in S whose length is at least N, there exists a second word B of the same length as A, such that the event that B appears before A in the sequence X1, X2,… has greater probability than that of A appearing before B. In this paper it is shown that a distribution ℙ satisfies Pevzner's conclusion if and only if the maximum value of ℙ, p, and the secondary maximum c satisfy the inequality . For |S| = 2 or |S| = 3, the inequality is true and the conjecture holds. If , then the conjecture is true when A is not allowed to consist of pure repetitions of that unique element for which the distribution takes on its mode.

Type
Research Article
Information
Combinatorics, Probability and Computing , Volume 4 , Issue 3 , September 1995 , pp. 279 - 285
Copyright
Copyright © Cambridge University Press 1995

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