A Serre spectral sequence for the moduli space of tropical curves
Christin Bibby, Melody Chan, Nir Gadish, Claudia He Yun · Journal of Combinatorial Algebra · 2017
Let S be a generating set of a finitely generated group G = \langle S \rangle . Denote by a_n the number of words in S of length n that are equal to 1. We show that the cogrowth sequence \{a_n\} is not always P-recursive. This is done by developing new combinatorial tools and using known results in computability and probability on groups.