PAPER / ARXIV:2609.09514
N. D. Khodyunya
RESUMO
We give an explicit finite sum for the number of ideals of the Lie algebra of strictly lower triangular $n\times n$ matrices over $\mathbb F_q$, valid for every prime power $q$. The sum runs over integer compositions, with weights expressed using ordinary and Gaussian binomial coefficients. A contraction bijection transforms Gagnon's configuration sum into a weighted enumeration of nonnesting partitions, with antichains of intervals chosen independently in each block. We derive a Stieltjes continued fraction for the block weights. Lagrange inversion and the coefficient formula for Stieltjes--Rogers polynomials then yield the explicit sum.
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