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1.iv. History of the conjectures

Soon after Sottile obtained the results of his thesis [So94], Boris Shapiro and Michael Shapiro formulated a very general, but precise conjecture, which dealt with this phenomenon of reality in enumerative geometry for Grassmannians. (Here are excerpts from letters giving more information.) Their conjecture was also concerned with the flag manifold. As stated, it is false - we describe a counterexample later.

   Restricting their conjecture to Grassmannians shows a relation to part of the static pole placement problem of linear systems theory. This relation is described in more detail in [So98]. While studying the pole placement problem numerically [RS], Rosenthal and Sottile decided to test some instances of the conjecture of Shapiro and Shapiro. Much to their surprise, the computations were all in agreement with the conjecture. (Here is a description of that project.)

   In the aftermath of those computations, restricted versions of the conjecture have appeared in print [RS, So97c,HSS]. Also, Sottile distributed two challenges to the systems solving community. One concerned `hypersurface' Schubert conditions (see Section 2), and the second concerned `Pieri-type' Schubert conditions (see Section 3). A spectacular symbolic computation of Faugère, Rouillier, and Zimmermann [FRZ] was in response to these challenges. They verified one instance of the conjecture involving the 462 4-planes meeting 12 3-panes in 7-space. This renewed Sottile's interest in these conjectures and inspired the recent work. To the best of our knowledge, this document and the paper [So98] mark the debut in print of the most general version of the conjecture of Shapiro and Shapiro.