Computing Reviews

A palindromization map for the free group
Kassel C., Reutenauer C. Theoretical Computer Science409(3):461-470,2008.Type:Article
Date Reviewed: 04/13/09

This paper is in the area of discrete mathematics. It describes a self map of a free group, referred to as a palindromization map (Pal). Various properties of Pal are proved: braid groups, profinite topology, and cohomological interpretations.

Section 0 briefly explains Pal with background literature. The free group, denoted by F2, is generated by a two-letter alphabet and involves right iterated palindromic closures. Section 1 describes a class of automorphisms on F2 and proves a lemma. Section 2 explains group homomorphisms involving braid group B3 and automorphisms on F2. Section 3 describes an equation of Pal and its interpretation in the language of Serre’s non-Abelian cohomology; the appendix presents Serre’s non-Abelian cohomology. Section 4 proves the main contributions of the paper: the connection of Pal with F2 and the extension to right iterated palindromic closure. Section 5 presents the conditions for Pals to be equal. Section 7 proves a conjugation property involving image Pal(F2). In addition, a theorem is presented that states that a subset of Pal(F2) is closed in F2 for the profinite topology. Background for the proof is developed in Section 5.

Understanding this paper requires a strong background and interest in discrete mathematical structures.

Reviewer:  Maulik A. Dave Review #: CR136679 (0911-1064)

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