Problem 4: Twelve people are seated around a circular table. In how many ways can six pairs of people engage in handshakes so that no arms cross? (Nobody is allowed to shake hands with more than one person at once)
The solution given in the book A Mathematical Olympiad Primer by Geoff Smith makes use of the Catalan Sequence. However, I don't see the linkage between the Catalan Sequence and the question. Does anyone know how they are linked?