The choice between these two options determines which partial embedding gets returned,
and therefore, which partial embedding gets extended to the embedding of S. The
consequences of both choices are continued here, keeping the choices consistent whenever
possible in the future to exemplify how two different embeddings can be obtained from the
same PC-Tree.
Next the algorithm embeds the back neighborhood of 9. The choice of embedding in the
previous step forces the algorithm to embed the edges incident to 9 in a different order. See
Figure 2.15.