On the number of palindromic factors of low complexity words

RESUMO

Factor complexity counts the distinct factors of each length in an infinite word, while palindromic complexity counts those invariant under reversal. For recurrent aperiodic words with reversal-closed language, the total number of palindromic factors in two consecutive lengths is at most the one-step growth of factor complexity plus two. We prove that equality is forced whenever the factor complexity at a given length does not exceed three halves of that length plus one. We construct examples showing that the bound is optimal. We also obtain an adaptive local criterion and consequences for reversal-closed quasi-Sturmian words and palindromic defect.