Schubert calculus

Summary

Schubert calculus is the computation of intersections of Schubert varieties in Grassmannians and flag varieties. It works in the cohomology ring, or the Chow ring, where the classes of Schubert varieties form a basis. The products of these classes are given by the Pieri rule and by Littlewood–Richardson coefficients. It answers classical questions of enumerative geometry, such as how many lines meet four general lines in space.