... enumerations and generating functions for permutations which avoid 1243, 2143, and certain additionalpatterns. We also give generating functions for permutations which avoid 1243 and 2143 and contain ... permutations which avoid 132, continued fractions, and Chebyshev polynomials of the second kind. In thispaper we prove analogues of some of these results for permutations which avoid 1243 and 2143. ... partition S (1243, 2143, 321) into the following four sets:T1= {π ∈ S (1243, 2143, 231) ||π|≤3};T2= {π ∈ S (1243, 2143, 231) ||π|≥ 4and (1) = |π|};T3= {π ∈ S (1243, 2143, 231) ||π|≥ 4and (2) =...