Kraśkiewicz–Pragacz modules and Ringel duality

In [5] and [6] Kraśkiewicz and Pragacz introduced representations of the upper-triangular Lie algebra bb whose characters are Schubert polynomials. In [12] the author studied the properties of Kraśkiewicz–Pragacz modules using the theory of highest weight categories. From the results there, in particular we obtain a certain highest weight category whose standard modules are KP modules. In this paper we show that this highest weight category is self Ringel-dual. This leads to an interesting symmetry relation on Ext groups between KP modules. We also show that the tensor product operation on bb-modules is compatible with Ringel duality functor.