Avoiding and Enforcing Repetitive Structures in Words 53 " nor as "a plant

" nor as "a plant that cometh of the lust of the earth

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Der Anreiz

Avoiding and Enforcing Repetitive Structures in Words 53 " nor as "a plantAvoiding and enforcing repetitions in words are central topics in the area of combinatorics on words, with first results going back to the beginning of the 20th century. The results presented in this thesis extend and enrich the existing theory concerning the presence and absence of repetitive structures in words. In the first part the question whether such structures necessarily appear in infinite words over a finite alphabet is investigated. In