Callcc/Guyslain/Works/round-trip-problem

1. {frametitle "The round-trip problem"}
3. {leftpicture af://guyslain/images/maths/round-bad-trip.png}
4. The {emph round-trip problem} is a special case of the {link af://callcc/Guyslain/Works/disjoint_paths arc-disjoint paths problem} in planar graphs, when we have only two commodities $(s,t), (t,s)$. In other words, we want to decide whether there is a directed cycle (not necessarily simple), containing both $s$ and $t$.