Sorting Networks: the End Game
  This paper studies properties of the back end of a sorting network and illustrates the utility of these in the search for networks of optimal size or depth. All previous works focus on properties of the front end of networks and on how to apply these to break symmetries in the search. The new properties help shed understanding on how sorting networks sort and speed-up solvers for both optimal size and depth by an order of magnitude. 
Michael Codish and Lu\'is Cruz-Filipe and Peter Schneider-Kamp
cs.DS