“…For some words and families of words, for example, Sturmian words, the equality holds: Ω(x) = A(x). Moreover, the property Ω(x) = A(x) characterizes Sturmian words among uniformly recurrent binary words [13]. On the other hand, it is easy to see that the abelian closure of the Thue-Morse word TM, defined as the fixed point (starting with 0) of the morphism 0 → 01, 1 → 10, is {ε, 0, 1} • {01, 10} N (see, e.g., [13] for a proof.)…”