Quantum Schubert Calculus

This paper works out the versions of the classical Giambelli and Pieri formulas in the context of quantum cohomology of a complex Grassmannian.Comment: 20 pages (LaTeX). To appear in Advances in Mathematics. The quantum Pieri formula in the original version has been corrected (see also alg-geom/9705024), and the Title has been ``quantized'

Simplicial Differential Calculus, Divided Differences, and Construction of Weil Functors

We define a simplicial differential calculus by generalizing divided differences from the case of curves to the case of general maps, defined on general topological vector spaces, or even on modules over a topological ring K. This calculus has the advantage that the number of evaluation points growths linearly with the degree, and not exponentially as in the classical, "cubic" approach. In particular, it is better adapted to the case of positive characteristic, where it permits to define Weil functors corresponding to scalar extension from K to truncated polynomial rings K[X]/(X^{k+1}).Comment: V2: minor changes, and chapter 3: new results included; to appear in Forum Mathematicu