Give an example of a bipartite connected graph which has an even number of vertices and an Eulerian circuit, but does not have a perfect matching.
2026-03-26 20:26:07.1774556767
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Bipartite Connected Graph, Eulerian Circuit
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Hint: In a bipartite graph, any edge in a matching must go from one half to the other. Using only this fact, can you think of a very simple criterion on a bipartite graph that will ensure that there is no perfect matching? Finding one such graph which also fulfills the other two requirements should be rather easy.
Bipartite ... Only Red and Blue vertices are joined.
An even number of vertices ... $3+5=8$.
Eulerian ... each vertex has even valency.
But ... there is clearly no matching.