On triangulating k-outerplanar graphs

A k-outerplanar graph is a graph that can be drawn in the plane without crossing such that after k-fold removal of the vertices on the outer-face there are no vertices left. In this paper, we study how to triangulate a k-outerplanar graph while keeping its outerplanarity small. Specifically, we show that not all k-outerplanar graphs can be triangulated so that the result is k-outerplanar, but they can be triangulated so that the result is (k+1)-outerplanar.