# Diameter of Cayley graphs of subgroups of $S_n$ without inverses

Babai and Seress proved that given a subgroup $G \leq S_n$ and a generating set $S$ of $G$, any permutation in $G$ can be written as a product of generators and their inverses of length $e^{(1+o(1))\sqrt{n\log n}}$. This bound is optimal since $S_n$ has an element of order $e^{(1+o(1))\sqrt{n\log n}}$.

The classical fact that every element in $S_n$ has order at most $e^{(1+o(1))\sqrt{n\log n}}$, combined with the result of Babai and Seress, shows that given a subgroup $G \leq S_n$ and a generating set $S$ of $G$, any permutation in $G$ can be written as a product of generators of length at most $e^{2(1+o(1))\sqrt{n\log n}}$.

Can we improve the upper bound $e^{2(1+o(1))\sqrt{n\log n}}$ to $e^{(1+o(1))\sqrt{n\log n}}$?

This question has been inspired by the recent question Automata and a kind of pumping lemma on state transition function.

The answer is yes, we can improve the upper bound to $\mathrm{e}^{(1 + o(1))\sqrt{n\ln n}}$. It was proved in a more recent paper of Babai (Corollary 2.9).