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| | NewAbelianSquare-FreeTD0L-LanguagesOver4Letters.nb |
 | | As mentioned above, the systematic study of word structures, i.e., combinatorics on words, was started by Axel Thue (1863--1922) in [34] at the beginning of the 20th century. |
 | | Unfortunately, Thue's results were forgotten for a long time, and they have been rediscovered and republished again and again -- at least dozen times as noted in [9]. |
 | | In a paper from 1961, see [13, p.240], Paul Erdös (1913--1996) raised the question whether abelian squares can be avoided in infinitely long words, i.e., whether there exist infinitely many abelian square-free words over a given alphabet. |
| south.rotol.ramk.fi /keranen/ias2002/NewAbelianSquare-FreeTD0L-LanguagesOver4Letters.html (3653 words) |
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