The undirected graph is isomorphic to this bipartite graph:

  U: { a, b, x }
  V: { e1, e2, e3 }
  E: { (a, e1), (b, e1), (b, e2), (c, e2), (c, e3), (a, e3) }

> But while that's technically true, that's also not really what people mean.

Not sure who these people are, but there are definitely cases where the bipartite form is useful.