  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.
