A congruence modulo four in real Schubert calculus with isotropic flags

Nickolas Hein, Frank Sottile, Igor Zelenko

Published 2014-05-30, updated 2015-02-05Version 2

We previously obtained a congruence modulo four for the number of real solutions to many Schubert problems on a square Grassmannian given by osculating flags. Here, we consider Schubert problems given by more general isotropic flags, and prove this congruence modulo four for the largest class of Schubert problems that could be expected to exhibit this congruence.