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Interval k-Graphs and Orders

机译:间隔k图和阶数

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An interval k-graph is the intersection graph of a family of intervals of the real line partitioned into k classes with vertices adjacent if and only if their corresponding intervals intersect and belong to different classes. In this paper we study the cocomparability interval k-graphs; that is, the interval k-graphs whose complements have a transitive orientation and are therefore the incomparability graphs of strict partial orders. For brevity we call these orders interval k-orders. We characterize the kind of interval representations a cocomparability interval k-graph must have, and identify the structure that guarantees an order is an interval k-order. The case k = 2 is peculiar: cocomparability interval 2-graphs (equivalently proper- or unit-interval bigraphs, bipartite permutation graphs, and complements of proper circular-arc graphs to name a few) have been characterized in many ways, but we show that analogous characterizations do not hold if k 2. We characterize the cocomparability interval 3-graphs via one forbidden subgraph and hence interval 3-orders via one forbidden suborder.
机译:间隔k图是当且仅当它们的相应间隔相交并属于不同类时,实线间隔家族的相交图,该实线间隔被划分为k个类,顶点相邻。在本文中,我们研究了可比区间k-图。就是说,间隔k图的补码具有传递方向,因此是严格偏序的不可比图。为简便起见,我们称这些阶为间隔k阶。我们表征了可比性间隔k图必须具有的间隔表示的种类,并确定保证阶数为间隔k阶的结构。 k = 2的情况是奇特的:可比较间隔2图(等价的固有区间图或单位区间的有向图,二分置换图,以及适当的圆弧图的补全,仅举几例)已被表征,但是我们展示了如果k> 2,类似的表征将不成立。我们通过一个禁止子图来描述可比间隔3图,并因此通过一个禁止子图来描述间隔3阶。

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