When this condition is verified an upwa_plan_undi_graph upug is built, possibly adding a minimum number of switches (sources and sinks) on some edges. In this case, these dummy nodes (that we call "bends") are atumatically removed when passing upug to a draw_undi_graph object; drawings so obtained are called "quasi-upward drawings". An upward drawing is a quasi-upward drawing without bends.

Observe that this class is very similar to the orth_plan_undi one.

Three different kinds of 'bend_constraint' are possible for an edge:

- ANY = any number of bends on edge;
- NONE = no bends on edge;
- MINIMAL = a 'minimal' number of bends on edge (default).

- PLAN_UPWARD_OPTIMAL: finds an upug with the minimum number of bends, preserving the embedding. (Polynomial)
- PLAN_UPWARD_SLOW : finds an upug with the minimum number of bends, searching over all possible planar embeddings of the graphs. It is an exponential-time algorithm based on branch and bound techniques, and currently works for biconnected graphs only.

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