Special matchings and permutations in Bruhat orders

For any permutation v, we show that the special matchings of v generate a Coxeter system. This gives new necessary conditions on an abstract poset to be isomorphic to a lower Bruhat interval of the symmetric group, and also answers in the affirmative, in the symmetric group case, a problem posed in [F. Brenti, F. Caselli, M. Marietti, Special matchings and Kazhdan-Lusztig polynomials, Adv. Math. 202 (2006) 555601]. (c) 2006 Elsevier Inc. All rights reserved