The theory of Gr bner bases is a main tool for dealing with rings of differential operators. This book reexamines the concept of Gr bner bases from the point of view of geometric deformations. The algorithmic methods introduced in this book are particularly useful for studying the systems of multidimensional hypergeometric PDE's introduced by Gelfand, Kapranov, and Zelevinsky. A number of original research results are contained in the book, and many...