... 83trail, 28transversal, 36 tree, 17triangle, 71triangle-free, 51triangulation, 71trivial graph, 9trivial path, 112-cell, 76 2-switch, 7 6. 1 Digraphs 87Consider a multidigraph with for which ... (circles), 68 Kuratowski graph, 61 latin rectangle, 37latin square, 37leaf, 7line segment graph, 69 linked cycles, 77list chromatic number, 67 list colouring, 67 loop, 4Möbius band, 71map, 65 matching, ... ( -) improvable, if .On the right, the bold path has value,and therefore this path is improvable. 6. 1 Digraphs 86 DEFINITION. A graph is di-orientable, if there is a di-connected oriented graph...