In mathematics, list edge-coloring is a type of graph coloring that combines list coloring and edge coloring. An instance of a list edge-coloring problem consists of a graph together with a list of allowed colors for each edge. A list edge-coloring is a choice of a color for each edge, from its list of allowed colors; a coloring is proper if no two adjacent edges receive the same color.
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A graph G is k-edge-choosable if every instance of list edge-coloring that has G as its underlying graph and that provides at least k allowed colors for each edge of G has a proper coloring. The edge choosability, or list edge colorability, list edge chromatic number, or list chromatic index, ch′(G) of graph G is the least number k such that G is k-edge-choosable. It is conjectured that it always equals the chromatic index.
Properties
Some properties of ch′(G):
- ch′(G) < 2 χ′(G).
- ch′(Kn,n) = n. This is the Dinitz conjecture, proven by Galvin (1995).
- ch′(G) < (1 + o(1))χ′(G), i.e. the list chromatic index and the chromatic index agree asymptotically (Kahn 2000).
Here χ′(G) is the chromatic index of G; and Kn,n, the complete bipartite graph with equal partite sets.
List coloring conjecture
The most famous open problem about list edge-coloring is probably the list coloring conjecture.
ch′(G) = χ′(G).This conjecture has a fuzzy origin; Jensen & Toft (1995) overview its history. The Dinitz conjecture, proven by Galvin (1995), is the special case of the list coloring conjecture for the complete bipartite graphs Kn,n.