The equidistribution of some length-three vincular patterns on Sn(132)

Abstract

In 2012 Bóna showed the rather surprising fact that the cumulative number of occurrences of the classical patterns 231 and 213 is the same on the set of permutations avoiding 132, even though the pattern based statistics 231 and 213 do not have the same distribution on this set. Here we show that if it is required for the symbols playing the role of 1 and 3 in the occurrences of 231 and 213 to be adjacent, then the obtained statistics are equidistributed on the set of 132-avoiding permutations. Actually, expressed in terms of vincular patterns, we prove bijectively the following more general results: the statistics based on the patterns ▪, ▪ and ▪, together with other statistics, have the same joint distribution on Sn(132), and so do the patterns ▪ and ▪; and up to trivial transformations, these statistics are the only based on length-three proper (not classical nor consecutive) vincular patterns which are equidistributed on a set of permutations avoiding a classical length-three pattern.