On the diagram of Schroeder permutations
  Egge and Mansour have recently studied permutations which avoid 1243 and 2143 regarding the occurrence of certain additional patterns. Some of the open questions related to their work can easily be answered by using permutation diagrams. Like for 132-avoiding permutations the diagram approach gives insights into the structure of {1243,2143}-avoiding permutations that yield simple proofs for some enumerative results concerning forbidden patterns in such permutations. 
Astrid Reifegerste