We consider the problem of finding the repetitive structures of a give
n string x. The period u of the string x grasps the repetitiveness of
x, since x is a prefix of a string constructed by concatenations of u.
We generalize the concept of repetitiveness as follows: A string w co
vers a string I if there is a superstring of x which is constructed by
concatenations and superpositions of Lu. A substring w of x is called
a seed of x if w covers x. we present an O (n log n)-time algorithm f
or finding all the seeds of a given string of length n.