Group Actions and Some Combinatorics on Words with $\mathbf{vtm}$

Abstract

We introduce generalizations of powers and factor complexity via orbits of group actions. These generalizations include concepts like abelian powers and abelian complexity. It is shown that this notion of factor complexity cannot be used to recognize Sturmian words in general. Within our framework, we establish square avoidance results for the ternary squarefree Thue--Morse word $\mathbf{vtm}$. These results go beyond the usual squarefreeness of $\mathbf{vtm}$ and are proved using Walnut. Lastly, we establish a group action factor complexity formula for $\mathbf{vtm}$ that is expressed in terms of the abelian complexity of the period doubling word $\mathbf{pd}$.