vexillary permutation

== English == === Etymology === So called because they are related to flags of modules. === Noun === vexillary permutation (plural vexillary permutations) (mathematics) A permutation μ of the positive integers containing no subpermutation isomorphic to the permutation (2143); in other words, there do not exist four numbers i < j < k < l with μ(j) < μ(i) < μ(l) < μ(k).