Sums of Schubert structure constants with bounded Coxeter length

Abstract

<jats:p> Pak–Robichaux recently introduced a signed puzzle rule for Schubert structure constants, which they use to show that sums <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>γ</mml:mi> <mml:mi>k</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> of these constants with a bounded number of inversions are polynomial. We give a different, conceptual proof that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>γ</mml:mi> <mml:mi>k</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> is (eventually) polynomial, which computes its lead term and extends to all classical Lie types. </jats:p>