Weakly self-avoiding words and a construction of Friedman.
Well quasi-orders, unavoidable sets, and derivation systems
Let I be a finite set of words and be the derivation relation generated by the set of productions {ε → u | u ∈ I}. Let be the set of words u such that . We prove that the set I is unavoidable if and only if the relation is a well quasi-order on the set . This result generalizes a theorem of [Ehrenfeucht et al.,Theor. Comput. Sci.27 (1983) 311–332]. Further generalizations are investigated.
Words and repeated factors.
Words over an ordered alphabet and suffix permutations
Given an ordered alphabet and a permutation, according to the lexicographic order, on the set of suffixes of a word , we present in this article a linear time and space method to determine whether a word has the same permutation on its suffixes. Using this method, we are then also able to build the class of all the words having the same permutation on their suffixes, first of all the smallest one. Finally, we note that this work can lead to a method for generating a Lyndon word randomly in linear...
Words over an ordered alphabet and suffix permutations
Given an ordered alphabet and a permutation, according to the lexicographic order, on the set of suffixes of a word w, we present in this article a linear time and space method to determine whether a word w' has the same permutation on its suffixes. Using this method, we are then also able to build the class of all the words having the same permutation on their suffixes, first of all the smallest one. Finally, we note that this work can lead to a method for generating a Lyndon word...
Words with simple Burrows-Wheeler transforms.
Об одном классе формальных языков.
Синтаксические полугруппы избегаемых языков