Estéban Gabory, Eric Rivals, Michelle Sweering, Hilde Verbeek and Pengfei Wang
Periodicity of Degenerate Strings
Abstract: 
The notion of periods is key in stringology, word combinatorics, and pattern
matching algorithms. A string has period p if every two letters
at distance p from each other are equal.
There has been a growing interest in more general models of sequences which
can describe uncertainty. An important model of sequences with uncertainty
are degenerate strings. A degenerate string is a string with "undetermined"
symbols, which can denote arbitrary subsets of the alphabet Σ.
Degenerate strings have been extensively used to describe uncertainty in DNA,
RNA, and protein sequences using the IUPAC code (Biochemistry, 1970).
In this work, we extend the work of Blanchet–Sadri et al. (2010)
to obtain the following results about the combinatorial aspects of periodicity
for degenerate strings:

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