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tim-at-topos committed Apr 18, 2024
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10 changes: 4 additions & 6 deletions trees/sga1/sga1-i/sga1-i.10.tree
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Expand Up @@ -83,18 +83,16 @@
Then
}

\todo{the following list should be i, ii, etc}

\ol{
\li{
\olc{
\lic{i.}{
#{K} is unramified over #{Y}.
}

\li{
\lic{ii.}{
If #{L} is an extension of #{K} that is unramified over #{Y}, and if #{Y'} is a normal prescheme, of field #{L}, that dominates #{Y} (e.g. the normalisation of #{Y} in #{L}), and #{M} an extension of #{L} that is unramified over #{Y'}, then #{M/K} is unramified over #{X} (this is the \em{transitivity} property).
}

\li{
\lic{iii.}{
Let #{Y'} be a normal integral prescheme that dominates #{Y}, of field #{K'/K};
if #{L} is an extension of #{K} that is unramified over #{Y}, then #{L\otimes_K K'} is an extension of #{K'} that is unramified over #{Y'} (this is the \em{translation} property).
}
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10 changes: 3 additions & 7 deletions trees/sga1/sga1-i/sga1-i.11.tree
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Expand Up @@ -11,12 +11,8 @@
Here are two examples of this fact.
}

\p{
\todo{the following list should be a, b}
}

\ol{
\li{
\olc{
\lic{a.}{
Let #{C} be an algebraic curve with an ordinary double point #{x}, and let #{C'} be its normalisation, with #{a} and #{b} the two points of #{C'} over #{x}.
Let #{C'_1} and #{C'_2} be copies of #{C'}, with #{a_i} (resp. #{b_i}) the point of #{C'_i} corresponding to #{a} (resp. #{b}).
In the curve #{C'_1\coprod C'_2}, we identify #{a_1} with #{b_2}, and #{a_2} with #{b_1} (we leave making this process of identification precise to the reader; it will be explained in Chapter VI of the multiplodoque, but, in the case of curves over an algebraically closed field, is already covered in Serre's book on algebraic curves).
Expand All @@ -27,7 +23,7 @@
We note that is was questions of this sort that gave birth to the "theory of descent" for schemes.
}

\li{
\lic{b.}{
\p{
Let #{A} be a complete integral local ring;
we know that its normalisation #{A'} is finite over #{A} (by Nagata), and is thus a complete semi-local ring, and thus local, since it is integral.
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10 changes: 4 additions & 6 deletions trees/sga1/sga1-i/sga1-i.2.tree
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Expand Up @@ -15,16 +15,14 @@
Then the following conditions are equivalent:
}

\p{\todo{the following list should be i, ii, etc}}

\ol{
\li{
\olc{
\lic{i.}{
#{B/\mathfrak{m}B} is of finite dimension over #{k=A/\mathfrak{m}}.
}
\li{
\lic{ii.}{
#{\mathfrak{m}B} is an ideal of definition, and #{B/\mathfrak{r}(B)=k(B)} is an extension of #{k=k(A)}.
}
\li{
\lic{iii.}{
The completion #{\widehat{B}} of #{B} is finite over the completion #{\widehat{A}} of #{A}.
}
}
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38 changes: 15 additions & 23 deletions trees/sga1/sga1-i/sga1-i.3.tree
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Expand Up @@ -15,16 +15,14 @@
Then the following conditions are equivalent:
}

\p{\todo{the following list should be i, ii, etc}}

\ol{
\li{
\olc{
\lic{i.}{
#{\sh{O}_x/\mathfrak{m}_y\sh{O}_x} is a finite separable extension of #{k(y)}.
}
\li{
\lic{ii.}{
#{\Omega_{X/Y}^1} is zero at #{x}.
}
\li{
\lic{iii.}{
The diagonal morphism #{\Delta_{X/Y}} is an open immersion on a neighbourhood of #{x}.
}
}
Expand All @@ -45,14 +43,12 @@
\number{I.3.2}
\taxon{definition}

\p{\todo{the following list should be a, b}}

\ol{
\li{
\olc{
\lic{a.}{
Let #{f} satisfy one of the equivalent conditions of \ref{sga1-i.3.1}.
Then we say that #{f} is \em{unramified} at #{x}, or that #{X} is unramified at #{x} on #{Y}.
}
\li{
\lic{b.}{
Let #{A\to B} be a local homomorphism.
We say that it is \em{unramified}, or that #{B} is a local \em{unramified} algebra on #{A}, if #{B/\mathfrak{r}(A)B} is a finite separable extension of #{A/\mathfrak{r}(A)}, i.e. if #{\mathfrak{r}(A)B=\mathfrak{r}(B)} and #{k(B)} is a separable extension of #{k(A)}.
(cf. regrets in [III 1.2])
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\number{I.3.5}
\taxon{proposition}

\p{\todo{the following list should be i, ii, etc}}

\ol{
\li{
\olc{
\lic{i.}{
An immersion is ramified.
}
\li{
\lic{ii.}{
The composition of two ramified morphisms is also ramified.
}
\li{
\lic{iii.}{
Base extension of a ramified morphisms is also ramified.
}
}
Expand All @@ -125,16 +119,14 @@
\number{I.3.6}
\taxon{corollary}

\p{\todo{the following list should be iv, v, etc}}

\ol{
\li{
\olc{
\lic{iv.}{
The cartesian product of two unramified morphisms is unramified.
}
\li{
\lic{v.}{
If #{gf} is unramified then so too is #{f}.
}
\li{
\lic{vi.}{
If #{f} is unramified then so too is #{f_\mathrm{red}}.
}
}
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20 changes: 7 additions & 13 deletions trees/sga1/sga1-i/sga1-i.4.tree
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Expand Up @@ -6,8 +6,6 @@
\import{sga1-macros}
\put\transclude/numbered{false}

\todo{fix the auto-capitalisation of the title not recognising É}

\p{
We are going to suppose that everything concerning flat morphisms that we need to be true is indeed true;
these facts will be proved later, if there is time.
Expand All @@ -18,16 +16,14 @@
\taxon{definition}
\number{I.4.1}

\todo{this list should be a, b}

\ol{
\li{
\olc{
\lic{a.}{
Let #{f\colon X\to Y} be a morphism of finite type.
We say that #{f} is \em{étale} at #{x} if #{f} is both flat and unramified at #{x}.
We say that #{f} is étale if it is étale at all points.
We say that #{X} is étale at #{x} over #{Y}, or that it is a #{Y}-prescheme which is étale at #{x} etc.
}
\li{
\lic{b.}{
Let #{f\colon A\to B} be a local homomorphism.
We say that #{f} is étale, or that #{B} is étale over #{A}, if #{B} is flat and unramified over #{A}
\footnote{cf. regrets in \fref{sga1-iii.1.2}.}
Expand Down Expand Up @@ -98,16 +94,14 @@
\taxon{proposition}
\number{I.4.6}

\todo{this list should be i, ii etc}

\ol{
\li{
\olc{
\lic{i.}{
An open immersion is étale.
}
\li{
\lic{ii.}{
The composition of two étale morphisms is étale.
}
\li{
\lic{iii.}{
The base extension of an étale morphism is étale.
}
}
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16 changes: 6 additions & 10 deletions trees/sga1/sga1-i/sga1-i.9.tree
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Expand Up @@ -115,13 +115,11 @@
Let #{f\colon A\to B} be a local homomorphism, with #{B} isomorphic to the localisation of an #{A}-algebra of finite type over #{A}.
}

\p{\todo{the following list should be i, ii}}

\ol{
\li{
\olc{
\lic{i.}{
If #{f} is étale, then #{A} is normal if and only if #{B} is normal.
}
\li{
\lic{ii.}{
If #{A} is normal, then #{f} is étale if and only if #{f} is injective and unramified (and then #{B} is normal, by (i)).
}
}
Expand All @@ -146,13 +144,11 @@
\subtree[sga1-i.9-serres-criterion]{
\title{Serre's criterion}

\p{\todo{the following list should be i, ii}}

\ol{
\li{
\olc{
\lic{i.}{
For every rank-#{1} prime ideal #{\mathfrak{p}} of #{A}, #{A_\mathfrak{p}} is normal (or, equivalently, regular);
}
\li{
\lic{ii.}{
For every rank-#{\geq2} prime ideal #{\mathfrak{p}} of #{A}, the depth of #{A_\mathfrak{p}} is #{\geq2}.
\footnote{cf. EGA IV 5.8.6.}
}
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9 changes: 9 additions & 0 deletions trees/sga1/sga1-macros.tree
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@@ -1,3 +1,12 @@
\xmlns:html{http://www.w3.org/1999/xhtml}

\def\olc[body]{
\<html:ol>{\body}
}
\def\lic[lbl][body]{
\<html:li>[style]{list-style-type: "\lbl "}{\body}
}

\def\tr{#{\operatorname{tr}}}
\def\Spec{#{\operatorname{Spec}}}
\def\Hom{#{\operatorname{Hom}}}
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58 changes: 35 additions & 23 deletions trees/sga6/sga6-0/sga6-0.1.tree
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Expand Up @@ -9,12 +9,17 @@
Recall the Riemann–Roch formula for a proper morphism
##{f\colon X\to Y}
of smooth quasi-projective schemes over a field #{k} and a coherent sheaf #{\sh{F}} on #{X}:
\todo{equation numbering}
##{
\Todd(T_Y)\ch_Y(f_*(\cl(\sh{F})))
= f_*(\Todd(T_X)\ch_X(\sh{F}))
\startverb\tag{1.1}\stopverb

\subtree[sga6-0.1-equation-1.1]{
\taxon{equation}
\number{1.1}
##{
\Todd(T_Y)\ch_Y(f_*(\cl(\sh{F})))
= f_*(\Todd(T_X)\ch_X(\sh{F}))
\startverb\tag{1.1}\stopverb
}
}

where #{\cl(\sh{F})} denotes the class of #{\sh{F}} in the group #{K(X)} of classes of coherent sheaves on #{X}, and #{\ch_X} and #{\ch_Y} denote the Chern characters of on #{X} and #{Y} (resp.), and #{T_X} and #{T_Y} the tangent bundles to #{X} and #{Y} (resp.).
This formula holds in #{A(Y)\otimes_\ZZ\QQ}, where #{A(Y)} is the Chow ring of #{Y};
the #{f_*} on the right-hand side is induced by tensoring with #{\QQ} the "direct image of cycles" homomorphism
Expand All @@ -28,18 +33,29 @@
}
As we know, #{\Todd(-)} and #{\ch(-)} are universal polynomials in the Chern classes of the argument with coefficients in #{\QQ}.
Since the constant term of #{\Todd(-)} is #{1}, it is an invertible element for any value of the argument, so that Equation (1.1) can be rewritten, after multiplication by #{\Todd(T_Y)^{-1}}, in the form which is more useful for our needs:
\todo{equation numbering}
##{
\ch_Y(f_*(\cl(\sh{F})))
= f_*(\Todd(T_f)\ch_X(\sh{F}))
\startverb\tag{1.2}\stopverb

\subtree[sga6-0.1-equation-1.2]{
\taxon{equation}
\number{1.2}
##{
\ch_Y(f_*(\cl(\sh{F})))
= f_*(\Todd(T_f)\ch_X(\sh{F}))
\startverb\tag{1.2}\stopverb
}
}

where we set
##{
T_f
= T_X - f^*(T_Y) \in K(X)
\startverb\tag{1.3}\stopverb

\subtree[sga6-0.1-equation-1.3]{
\taxon{equation}
\number{1.3}
##{
T_f
= T_X - f^*(T_Y) \in K(X)
\startverb\tag{1.3}\stopverb
}
}

so that #{T_f} plays the role of a \em{virtual relative tangent bundle} of #{X} over #{Y}.
In the case where the morphism #{f} is smooth (i.e. with everywhere-surjective tangent map), we have simply
##{
Expand All @@ -58,13 +74,11 @@
One of the main goals of this Seminar is to generalise Equation (1.2) simultaneously in two directions:
}

\todo{this list should be a, b}

\ol{
\li{
\olc{
\lic{a.}{
Remove the hypothesis of the existence of a base field #{k}.
}
\li{
\lic{b.}{
Replace the regularity hypotheses on #{Y} and #{X} by a "local regularity" hypothesis on #{f}.
}
}
Expand All @@ -73,10 +87,8 @@
Finally, along the way, we will equally deal with the problem:
}

\todo{this list should be c}

\ol{
\li{
\olc{
\lic{c.}{
Remove the quasi-projectivity hypotheses which, in the absence of a base field, are expressed by the existence of ample invertible modules on #{X} and on #{Y}.
}
}
8 changes: 3 additions & 5 deletions trees/sga6/sga6-i/sga6-i.0.tree
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Expand Up @@ -81,13 +81,11 @@
this theorem is, in reality, a conjecture, but has nevertheless been proven in the two particular following cases:
}

\p{\todo{the following list should be a, b}}

\ol{
\li{
\olc{
\lic{a.}{
#{S} is locally Noetherian;
}
\li{
\lic{b.}{
#{f} is projective.
}
}
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9 changes: 9 additions & 0 deletions trees/sga6/sga6-macros.tree
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@@ -1,3 +1,12 @@
\xmlns:html{http://www.w3.org/1999/xhtml}

\def\olc[body]{
\<html:ol>{\body}
}
\def\lic[lbl][body]{
\<html:li>[style]{list-style-type: "\lbl "}{\body}
}

\def\proof[body]{
\scope{
\put\transclude/toc{false}
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