[not] Le Monde puzzle
During a dinner of 20 couples sitting at four tables with ten seats, everyone wants to share a table with everyone. The assembly decides to switch seats after each serving towards this goal. What is the minimal number of servings needed to ensure that every couple shared a table with every other couple at some point? And what is the optimal switching strategy?
Of course, extension of the solution to k couples, n tables and p seats (with k<np) would be great!