isVexillary w
A permutation $p$ is vexillary if it is $2143$-avoiding.
i1 : p = permutation {3,1,2,5,4} o1 = Permutation{3, 1, 2, 5, 4} o1 : Permutation
i2 : isVexillary p o2 = false
The object isVexillary is a method function.