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Normalize math commands
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We may want to introduce \SheafEnd at a later stage but for the moment
it seems we don't use it a whole lot
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aisejohan committed Sep 21, 2014
1 parent 99bc65e commit d8adf24
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22 changes: 11 additions & 11 deletions etale-cohomology.tex
Expand Up @@ -8411,10 +8411,10 @@ \section{The Brauer group of a scheme}
which have positive rank at every $s \in S$ such that
$$
\mathcal{A} \otimes_{\mathcal{O}_S}
\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{F})
\SheafHom_{\mathcal{O}_S}(\mathcal{F}, \mathcal{F})
\cong
\mathcal{B} \otimes_{\mathcal{O}_S}
\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{G})
\SheafHom_{\mathcal{O}_S}(\mathcal{G}, \mathcal{G})
$$
as $\mathcal{O}_S$-algebras. The {\it Brauer group} of
$S$ is the set $\text{Br}(S)$ of equivalence classes of Azumaya
Expand All @@ -8426,8 +8426,8 @@ \section{The Brauer group of a scheme}
Let $S$ be a scheme. Let $\mathcal{F}$ and $\mathcal{G}$ be finite locally
free sheaves of $\mathcal{O}_S$-modules of positive rank. If there
exists an isomorphism
$\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{F}) \cong
\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{G})$ of
$\SheafHom_{\mathcal{O}_S}(\mathcal{F}, \mathcal{F}) \cong
\SheafHom_{\mathcal{O}_S}(\mathcal{G}, \mathcal{G})$ of
$\mathcal{O}_S$-algebras, then there exists an invertible sheaf
$\mathcal{L}$ on $S$ such that
$\mathcal{F} \otimes_{\mathcal{O}_S} \mathcal{L} \cong \mathcal{G}$
Expand All @@ -8437,8 +8437,8 @@ \section{The Brauer group of a scheme}

\begin{proof}
Fix an isomorphism
$\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{F}) \to
\mathcal{E}\!{\it nd}_{\mathcal{O}_S}(\mathcal{F})$.
$\SheafHom_{\mathcal{O}_S}(\mathcal{F}, \mathcal{F}) \to
\SheafHom_{\mathcal{O}_S}(\mathcal{G}, \mathcal{G})$.
Consider the sheaf $\mathcal{L} \subset \SheafHom(\mathcal{F}, \mathcal{G})$
generated as an $\mathcal{O}_S$-module by the local isomorphisms
$\varphi : \mathcal{F} \to \mathcal{G}$ such that conjugation by
Expand Down Expand Up @@ -8468,7 +8468,7 @@ \section{The Brauer group of a scheme}

\begin{proof}
Choose an \'etale covering $\{U_i \to S\}$ and choose isomorphisms
$\mathcal{A}|_{U_i} \to \mathcal{E}\!{\it nd}(\mathcal{F}_i)$
$\mathcal{A}|_{U_i} \to \SheafHom(\mathcal{F}_i, \mathcal{F}_i)$
for some locally free $\mathcal{O}_{U_i}$-modules $\mathcal{F}_i$
of rank $d$. (We may assume $\mathcal{F}_i$ is free.) Consider the
composition
Expand All @@ -8482,11 +8482,11 @@ \section{The Brauer group of a scheme}
according to the sign character under the action of the symmetric group
on $d$ letters. Then $p_i^2 = p_i$ and the rank of $p_i$ is $1$.
Using the given isomorphism
$\mathcal{A}|_{U_i} \to \mathcal{E}\!{\it nd}(\mathcal{F}_i)$
$\mathcal{A}|_{U_i} \to \SheafHom(\mathcal{F}_i, \mathcal{F}_i)$
and the canonical isomorphism
$$
\mathcal{E}\!{\it nd}(\mathcal{F}_i)^{\otimes d} =
\mathcal{E}\!{\it nd}(\mathcal{F}_i^{\otimes d})
\SheafHom(\mathcal{F}_i, \mathcal{F}_i)^{\otimes d} =
\SheafHom(\mathcal{F}_i^{\otimes d}, \mathcal{F}_i^{\otimes d})
$$
we may think of $p_i$ as a section of $\mathcal{A}^{\otimes d}$
over $U_i$. We claim that $p_i|_{U_i \times_S U_j} = p_j|_{U_i \times_S U_j}$
Expand All @@ -8509,7 +8509,7 @@ \section{The Brauer group of a scheme}
$$
is a locally free module of rank $d^d$ and that (left) multiplication
by $\mathcal{A}^{\otimes d}$ induces an isomorphism
$\mathcal{A}^{\otimes d} \to \mathcal{E}\!{\it nd}(\mathcal{H})$.
$\mathcal{A}^{\otimes d} \to \SheafHom(\mathcal{H}, \mathcal{H})$.
In other words, $\mathcal{A}^{\otimes d}$ is the trivial element
of the Brauer group of $S$ as desired.
\end{proof}
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12 changes: 6 additions & 6 deletions formal-spaces.tex
Expand Up @@ -752,7 +752,7 @@ \section{Topological rings and modules}
systems of open submodules in $M$ and $N$.
The {\it completed tensor product}
$$
M \widehat\otimes_R N =
M \widehat{\otimes}_R N =
\lim M \otimes_R N/(M_\mu \otimes_R N + M \otimes_R N_\nu) =
\lim M/M_\mu \otimes_R N/N_\nu
$$
Expand All @@ -765,7 +765,7 @@ \section{Topological rings and modules}
If $R \to A$ and $R \to B$ are continuous maps of
linearly topologized rings, then the construction above
gives a tensor product $A \otimes_R B$ and a completed
tensor product $A \widehat\otimes_R B$.
tensor product $A \widehat{\otimes}_R B$.

\medskip\noindent
We record here the notions introduced in Remark \ref{remark-mcquillan}.
Expand Down Expand Up @@ -856,7 +856,7 @@ \section{Topological rings and modules}
\label{lemma-closure-image-ideal}
Let $A \to B$ be a continuous map of linearly topologized rings.
Let $I \subset A$ be an ideal. The closure of $IB$
is the kernel of $B \to B \widehat\otimes_A A/I$.
is the kernel of $B \to B \widehat{\otimes}_A A/I$.
\end{lemma}

\begin{proof}
Expand All @@ -865,7 +865,7 @@ \section{Topological rings and modules}
Let $I_\mu$ be a fundamental system of open ideals in $A$.
Then
$$
B \widehat\otimes_A A/I = \lim (B/J_\lambda \otimes_A A/(I_\mu + I)) =
B \widehat{\otimes}_A A/I = \lim (B/J_\lambda \otimes_A A/(I_\mu + I)) =
\lim B/(J_\lambda + I_\mu B + I B)
$$
Since $A \to B$ is continuous, for every $\lambda$ there
Expand Down Expand Up @@ -2248,7 +2248,7 @@ \section{Separation axioms for formal algebraic spaces}
\item If $X$, $Y$, and $Z$ are McQuillan formal algebraic spaces
corresponding to the weakly admissible topological $S$-algebras
$A$, $B$, and $C$, then $X \times_Z Y$ corresponds to
$A \widehat\otimes_C B$.
$A \widehat{\otimes}_C B$.
\end{enumerate}
\end{lemma}

Expand Down Expand Up @@ -2795,7 +2795,7 @@ \section{Morphisms representable by algebraic spaces}
}
$$
By Lemma \ref{lemma-fibre-product-affines-over-separated}
we see that $B/J(I) = B \widehat\otimes_A A/I$.
we see that $B/J(I) = B \widehat{\otimes}_A A/I$.
It follows that $J(I)$ is the closure of the ideal $\varphi(I)B$, see
Lemma \ref{lemma-closure-image-ideal}.
Since $\text{Spf}(A) = \colim \Spec(A/I)$ with $I$ as above,
Expand Down

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