Abstract:
Let $G$ be a strongly connected, aperiodic, two-out digraph with adjacency matrix $A$. Suppose $A=R+B$ are coloring matrices: that is, matrices that represent the functions induced by an edge-coloring of $G$. We introduce a matrix $\Delta=\frac12(R-B)$ and investigate its properties. A number of useful conditions involving $\Delta$ which either are equivalent to or imply a solution to the road coloring problem are derived.