Published online by Cambridge University Press: 20 November 2018
Let $\pi :X\,\to \,S$ be a finite type morphism of noetherian schemes. A smooth formal embedding of
$X$ (over
$S$) is a bijective closed immersion
$X\,\subset \,\mathfrak{X}$ , where
$\mathfrak{X}$ is a noetherian formal scheme, formally smooth over
$S$. An example of such an embedding is the formal completion
$\mathfrak{X}={{Y}_{/X}}$ where
$X\,\subset \,Y$ is an algebraic embedding. Smooth formal embeddings can be used to calculate algebraic De Rham(co)homology.
Our main application is an explicit construction of the Grothendieck residue complex when $S$ is a regular scheme. By definition the residue complex is the Cousin complex of
${{\pi }^{!}}{{O}_{S}}$, as in
$[\text{RD}]$. We start with
$\text{I-C}$. Huang's theory of pseudofunctors on modules with 0-dimensional support, which provides a graded sheaf
${{\oplus }_{q}}K_{X/S}^{q}.$
We then use smooth formal embeddings to obtain the coboundary operator
$\delta :K_{X/S}^{q}\to K_{X/S}^{q+1}.$
We exhibit a canonical isomorphism between the complex
$K_{X/S}^{\cdot },\delta $ and the residue complex of
$[\text{RD}]$. When
$\pi $ is equidimensional of dimension
$n$ and generically smooth we show that
${{\text{H}}^{-n}}K_{X/S}^{\cdot }$ is canonically isomorphic to to the sheaf of regular differentials of Kunz-Waldi
$[\text{KW}]$.
Another issue we discuss is Grothendieck Duality on a noetherian formal scheme $\mathfrak{X}$ . Our results on duality are used in the construction of
$K_{X/S}^{\cdot }$.
Incumbent of the Anna and Maurice Boukstein Career Development Chair.