The λ4-Connectivity of the Cartesian Product of Trees.

Given a connected graph [Formula: see text] and [Formula: see text] with [Formula: see text], an [Formula: see text]-tree is a such subgraph [Formula: see text] of [Formula: see text] that is a tree with [Formula: see text]. Two [Formula: see text]-trees [Formula: see text] and [Formula: see text] are edge-disjoint if [Formula: see text]. Let [Formula: see text] be the maximum size of a set of edge-disjoint [Formula: see text]-trees in [Formula: see text]. The [Formula: see text]-connectivity of [Formula: see text] is defined as [Formula: see text]. In this paper, we first show some structural properties of edge-disjoint [Formula: see text]-trees by Fan Lemma and König-ore Formula. Then, the [Formula: see text]-connectivity of the Cartesian product of trees is determined. That is, let [Formula: see text] be trees, then [Formula: see text] if [Formula: see text] for each [Formula: see text], otherwise [Formula: see text]. As corollaries, [Formula: see text]-connectivity for some graph classes such as hypercubes and meshes can be obtained directly.