Abstract
In this paper we consider arbitrary intervals in the left weak order on the symmetric group Sn. We show that the Lehmer codes of permutations in an interval form a distributive lattice under the product order. Furthermore, the rank-generating function of this distributive lattice matches that of the weak order interval. We construct a poset such that its lattice of order ideals is isomorphic to the lattice of Lehmer codes of permutations in the given interval. We show that there are at least \({\left(\lfloor {\frac{n}{2}} \rfloor \right)!}\) permutations in Sn that form a rank-symmetric interval in the weak order.
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