Geodesic
The depression of a graph and k-kernels
Discussiones Mathematicae. Graph Theory, Tome 34 (2014) no. 2, pp. 233-247.

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An edge ordering of a graph G is an injection f : E(G) → R, the set of real numbers. A path in G for which the edge ordering f increases along its edge sequence is called an f-ascent ; an f-ascent is maximal if it is not contained in a longer f-ascent. The depression of G is the smallest integer k such that any edge ordering f has a maximal f-ascent of length at most k. A k-kernel of a graph G is a set of vertices U ⊆ V (G) such that for any edge ordering f of G there exists a maximal f-ascent of length at most k which neither starts nor ends in U. Identifying a k-kernel of a graph G enables one to construct an infinite family of graphs from G which have depression at most k. We discuss various results related to the concept of k-kernels, including an improved upper bound for the depression of trees.
Keywords: edge ordering of a graph, increasing path, monotone path, depression 
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Schurch, Mark; Mynhardt, Christine. The depression of a graph and k-kernels. Discussiones Mathematicae. Graph Theory, Tome 34 (2014) no. 2, pp. 233-247. http://geodesic.mathdoc.fr/item/DMGT_2014_34_2_a2/

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