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Avoiding fractional powers over the natural numbers
Combinatorics · Submitted 9 Oct 2015
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We identify the structure of the lexicographically least $a/b$-power-free word for three infinite families of rationals $a/b$ as well many "sporadic" rationals that do not seem to belong to general families.
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The abstract, sentence by sentence
We study the lexicographically least infinite $a/b$-power-free word on the alphabet of non-negative integers. Frequently this word is a fixed point of a uniform morphism, or closely related to one. For example, the lexicographically least $7/4$-power-free word is a fixed point of a $50847$-uniform morphism. We identify the structure of the lexicographically least $a/b$-power-free word for three infinite families of rationals $a/b$ as well many "sporadic" rationals that do not seem to belong to general families. To accomplish this, we develop an automated procedure for proving $a/b$-power-freeness for morphisms of a certain form, both for explicit and symbolic rational numbers $a/b$. Finally, we establish a connection to words on a finite alphabet. Namely, the lexicographically least $27/23$-power-free word is in fact a word on the finite alphabet $\{0, 1, 2\}$, and its sequence of letters is $353$-automatic.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We study the lexicographically least infinite $a/b$-power-free word on the alphabet of non-negative integers. | contribution 0.88 | 0.90 | 0.06 | asserted 0.93 |
| s1 | Frequently this word is a fixed point of a uniform morphism, or closely related to one. | result 0.74 | 0.53 | 0.06 | hedged possibility 0.63 |
| s2 | For example, the lexicographically least $7/4$-power-free word is a fixed point of a $50847$-uniform morphism. | result 0.98 | 0.81 | 0.07 | asserted 1.00 |
| s3 | We identify the structure of the lexicographically least $a/b$-power-free word for three infinite families of rationals $a/b$ as well many "sporadic" rationals that do not seem to belong to general families. | contribution 0.51 | 0.95 | 0.51 | asserted 0.99 |
| s4 | To accomplish this, we develop an automated procedure for proving $a/b$-power-freeness for morphisms of a certain form, both for explicit and symbolic rational numbers $a/b$. | method 0.98 | 0.96 | 0.07 | asserted 1.00 |
| s5 | Finally, we establish a connection to words on a finite alphabet. | result 0.54 | 0.90 | 0.11 | asserted 0.97 |
| s6 | Namely, the lexicographically least $27/23$-power-free word is in fact a word on the finite alphabet $\{0, 1, 2\}$, and its sequence of letters is $353$-automatic. | result 0.99 | 0.92 | 0.24 | asserted 1.00 |
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Original abstract
We study the lexicographically least infinite $a/b$-power-free word on the alphabet of non-negative integers. Frequently this word is a fixed point of a uniform morphism, or closely related to one. For example, the lexicographically least $7/4$-power-free word is a fixed point of a $50847$-uniform morphism. We identify the structure of the lexicographically least $a/b$-power-free word for three infinite families of rationals $a/b$ as well many "sporadic" rationals that do not seem to belong to general families. To accomplish this, we develop an automated procedure for proving $a/b$-power-freeness for morphisms of a certain form, both for explicit and symbolic rational numbers $a/b$. Finally, we establish a connection to words on a finite alphabet. Namely, the lexicographically least $27/23$-power-free word is in fact a word on the finite alphabet $\{0, 1, 2\}$, and its sequence of letters is $353$-automatic.
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