A Partially Synchronizing Coloring?

Given a nite directed graph, a coloring of its edges turns the graph into a nite-state automaton. A k-synchronizing word of a deterministic automaton is a word in the alphabet of colors at its edges that maps the state set of the automaton at least on k-element subset. A coloring of edges of a directed strongly connected nite graph of a uniform outdegree (constant outdegree of any vertex) is k-synchronizing if the coloring turns the graph into a deterministic nite automaton possessing a k-synchronizing word. For k = 1 one has the well known road coloring problem. The recent positive solution of the road coloring problem implies an elegant generalization considered rst by B eal and Perrin: a directed nite strongly connected graph of uniform outdegree is k-synchronizing i the greatest common divisor of lengths of all its cycles is k. Some consequences for coloring of an arbitrary nite digraph are presented. We describe a subquadratic algorithm of the road coloring for the k-synchronization implemented in the package TESTAS. A new linear visualization program demonstrates the obtained coloring. Some consequences for coloring of an arbitrary nite digraph and of such a graph of uniform outdegree are presented.