Morse and Hedlund’s Skew Sturmian Words Revisited

摘要

For any infinite word r over A = {a, b} we associate two infinite words min(r), max(r) such that any prefix of min(r) (max(r), respectively) is the lexicographically smallest (greatest, respectively) among the factors of r of the same length. We prove that (min(r); max(r)) = (as, bs) for some infinite word s if and only if r is a proper Sturmian word or an ultimately periodic word of a particular form. This result is based on a lemma concerning sequences of infinite words.