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arXiv · 0901.1397

Avoiding Squares and Overlaps Over the Natural Numbers

Mathieu Guay-Paquet·Jeffrey Shallit
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Abstract

We consider avoiding squares and overlaps over the natural numbers, using a greedy algorithm that chooses the least possible integer at each step; the word generated is lexicographically least among all such infinite words. In the case of avoiding squares, the word is 01020103..., the familiar ruler function, and is generated by iterating a uniform morphism. The case of overlaps is more challenging. We give an explicitly-defined morphism phi : N* -> N* that generates the lexicographically least infinite overlap-free word by iteration. Furthermore, we show that for all h,k in N with h <= k, the word phi^{k-h}(h) is the lexicographically least overlap-free word starting with the letter h and ending with the letter k, and give some of its symmetry properties.

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Mathieu Guay-Paquet, Jeffrey Shallit. 2009-01-12. Avoiding Squares and Overlaps Over the Natural Numbers. https://arxiv.org/abs/0901.1397

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