  Internal pattern matching requires one to answer queries about factors of a
given string. Many results are known on answering internal period queries,
asking for the periods of a given factor. In this paper we investigate (for the
first time) internal queries asking for covers (also known as quasiperiods) of
a given factor. We propose a data structure that answers such queries in
$O(\log n \log \log n)$ time for the shortest cover and in $O(\log n (\log \log
n)^2)$ time for a representation of all the covers, after $O(n \log n)$ time
and space preprocessing.

Data Structures and Algorithms