On the prefix-suffix duplication reduction

This work answers some questions proposed by Bottoni, Labella, and Mitrana (Theoretical Computer Science 682, 2017) regarding the prefix–suffix reduction on words. The operation is defined as a reduction by one half of every square that is present as either a prefix or a suffix of a word, leading thus to a finite set of words associated to the starting one. The iterated case considers consecutive applications of the operations, on all the resulting words. We show that the classes of linear and context-free language are closed under iterated bounded prefix–suffix square reduction, and that for a given word we can determine in O(n2 log n) time all of its primitive prefix–suffix square roots.