On the action of the symmetric group on the free LAnKe: a question of Friedmann, Hanlon, Stanley and Wachs

A LAnKe (also known as a Lie algebra of the $n$th kind, or a Filippov algebra) is a vector space equipped with a skew-symmetric $n$-linear form that satisfies the generalized Jacobi identity. The symmetric group ${\mathfrak{S}}_m$ acts on the multilinear part of the free LAnKe on $m=(n-1)k+1$ generators, where $k$ is the number of brackets, by permutation of the generators. The corresponding representation was studied by Friedmann, Hanlon, Stanley and Wachs, who asked whether for $n\ge k$, its irreducible decomposition contains no summand whose Young diagram has at most $k-1$ columns. The answer is affirmative if $k\le 3$. In this paper, we show that the answer is affirmative for all $k$. A proof has been given recently by Friedmann, Hanlon and Wachs. The two proofs are completely different.