A finite non-empty word z is said to be a border of a finite non-empty word w if w=uz=zv for some non-empty words u and v. A finite non-empty word is said to be bordered if it admits a border, and it is said to be unbordered otherwise. In this paper, we give two characterizations of the biinfinite words of the form ?uvu?, where u and v are finite words, in terms of its unbordered factors.The main result of the paper states that the words of the form ?uvu? are precisely the biinfinite words w=?a?2a?1a0a1a2? for which there exists a pair (l0,r0) of integers with l0
['Jose Costa']
Biinfinite words with maximal recurrent unbordered factors