The two sets <math>U</math> and <math>V</math> may be thought of as a coloring of the graph with two colors: if one colors all nodes in <math>U</math> blue, and all nodes in <math>V</math> green, each edge has endpoints of differing colors, as is required in the graph coloring problem.<ref name="s12">{{citation | year = 2012}}.</ref> In contrast, such a coloring is impossible in the case of a non-bipartite graph, such as a triangle: after one node is colored blue and another green, the third vertex of the triangle is connected to vertices of both colors, preventing it from being assigned either color. | The two sets <math>U</math> and <math>V</math> may be thought of as a coloring of the graph with two colors: if one colors all nodes in <math>U</math> blue, and all nodes in <math>V</math> green, each edge has endpoints of differing colors, as is required in the graph coloring problem.<ref name="s12">{{citation | year = 2012}}.</ref> In contrast, such a coloring is impossible in the case of a non-bipartite graph, such as a triangle: after one node is colored blue and another green, the third vertex of the triangle is connected to vertices of both colors, preventing it from being assigned either color. |