Rationality of the Möbius function of subword order
The subword ordering of words defines the Möbius function \(\mu: A^*\times A^*\to\mathbb{Z}\). The main result is that the noncommutative power series \(\sum_{\beta,\alpha\in A^*} \mu(\beta,\alpha)\beta\otimes\alpha\) is rational.
scientific article; zbMATH DE number 57558