square-free word

212 Views Asked by At

I am trying to understand one concept. Is it possible to have a square-free(no subwords ss) word in a language of just $\{0,1\}$ of any given length ( $10^{100}$ for instance). I found out a Thue–Morse sequence , but it is still not really the thing. If there is no such word , how to prove it?

1

There are 1 best solutions below

2
On BEST ANSWER

The longest square-free word for a language with a binary alphabet is of length 3. However, for alphabets of at least three symbols, there are infinitely many square-free words.

It's easy to prove the first assertion simply by enumerating all binary sequences of length four and observing that all of them contain a square. Since every word of length greater than four contains a subword of length 4, it must also contain a square (the one in the subword, at least).