Symmetric Chain Decompositions and the Strong Sperner Property for Noncrossing Partition Lattices

Henri Mühle (1)

1 LIX - Laboratoire d'informatique de l'École polytechnique [Palaiseau]

We prove that the noncrossing partition lattices associated with the complex reflection groups G(d, d, n) for d, n ≥ 2 admit a decomposition into saturated chains that are symmetric about the middle ranks. A consequence of this result is that these lattices have the strong Sperner property, which asserts that the cardinality of the union of the k largest antichains does not exceed the sum of the k largest ranks for all k ≤ n. Subsequently, we use a computer to complete the proof that any noncrossing partition lattice associated with a well-generated complex reflection group is strongly Sperner, thus affirmatively answering a special case of a question of D. Armstrong. This was previously established only for the Coxeter groups of type A and B.

Mots clés: Combinatorics

Domaines: Combinatoire [math.CO]

Henri Mühle. Symmetric Chain Decompositions and the Strong Sperner Property for Noncrossing Partition Lattices. 28-th International Conference on Formal Power Series and Algebraic Combinatorics, Simon Fraser University, Jul 2016, Vancouver, Canada. ⟨10.46298/dmtcs.6363⟩. ⟨hal-02166346⟩