A quadratic upper bound on the reset thresholds of synchronizing automata containing a transitive permutation group

Abstract

For any synchronizing $n$-state deterministic automaton, Černý conjectures the existence of a synchronizing word of length at most $(n-1{)}^2$. We prove that there exists a synchronizing word of length at most $2n^2-7n+7$ for every synchronizing $n$-state deterministic automaton that satisfies the following two properties: 1. The image of the action of each letter contains at least $n-1$ states; 2. The actions of bijective letters generate a transitive permutation group on the state set.