Precoloring extension in planar near-Eulerian-triangulations

Abstract

We consider the 4-precoloring extension problem in \emph{planar near-Eulerian- triangulations}, i.e., plane graphs where all faces except possibly for the outer one have length three, all vertices not incident with the outer face have even degree, and exactly the vertices incident with the outer face are precolored. We give a necessary topological condition for the precoloring to extend, and give a complete characterization when the outer face has length at most five and when all vertices of the outer face have odd degree and are colored using only three colors.