This book is aimed at students and researchers in commutative algebra,
algebraic geometry, and neighboring disciplines. The book will provide readers
with new insight into differential forms and may stimulate new research
through the many open questions it raises.
The authors introduce various sheaves of differential forms for
equidimensional morphisms of finite type between noetherian schemes, the most
important being the sheaf of regular differential forms. It is known in many
cases that the top degree regular differentials form a dualizing sheaf in the
sense of duality theory. All constructions in the book are purely local and
require only prerequisites from the theory of commutative noetherian rings and
their Kähler differentials. The authors study the relations between the
sheaves under consideration and give some applications to local properties of
morphisms. The investigation of the “fundamental class,” a
canonical homomorphism from Kähler to regular differential forms, is a
major topic. The book closes with applications to curve singularities.
While regular differential forms have been previously studied mainly in the
“absolute case” (that is, for algebraic varieties over fields),
this book deals with the relative situation. Moreover, the authors strive to
avoid “separability assumptions.” Once the construction of regular
differential forms is given, many results can be transferred from the absolute
to the relative case.