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\newtheorem{prop}{Proposition} \newtheorem{cor}{Corollary} \newtheorem*{utheorem}{Theorem} \newtheorem*{ulemma}{Lemma} \newtheorem*{uprop}{Proposition} \newtheorem*{ucor}{Corollary} \theoremstyle{definition} \newtheorem{defn}{Definition} \newtheorem{example}{Example} \newtheorem*{udefn}{Definition} \newtheorem*{uexample}{Example} \theoremstyle{remark} \newtheorem{remark}{Remark} \newtheorem{note}{Note} \newtheorem*{uremark}{Remark} \newtheorem*{unote}{Note} %------------------------------------------------------------------- \begin{document} %------------------------------------------------------------------- \section*{Introduction to Étale Cohomology} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{cohomology}{}\paragraph*{{Cohomology}}\label{cohomology} [[!include cohomology - contents]] \hypertarget{tale_morphisms}{}\paragraph*{{\'E{}tale morphisms}}\label{tale_morphisms} [[!include etale morphisms - contents]] This page collects links related to the textbook \begin{itemize}% \item [[Günter Tamme]], \emph{Introduction to \'E{}tale Cohomology} 1994 \end{itemize} on [[étale cohomology]]. \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{chapter_0_preliminaries}{Chapter 0 Preliminaries}\dotfill \pageref*{chapter_0_preliminaries} \linebreak \noindent\hyperlink{1_abelian_categories}{1. Abelian categories}\dotfill \pageref*{1_abelian_categories} \linebreak \noindent\hyperlink{2_homological_algebra_in_abelian_categories}{2. Homological algebra in abelian categories}\dotfill \pageref*{2_homological_algebra_in_abelian_categories} \linebreak \noindent\hyperlink{21_functors}{2.1 $\delta$-Functors}\dotfill \pageref*{21_functors} \linebreak \noindent\hyperlink{22_derived_functors}{2.2 Derived functors}\dotfill \pageref*{22_derived_functors} \linebreak \noindent\hyperlink{23_spectral_sequences}{2.3 Spectral sequences}\dotfill \pageref*{23_spectral_sequences} \linebreak \noindent\hyperlink{3_inductive_limits}{3. Inductive limits}\dotfill \pageref*{3_inductive_limits} \linebreak \noindent\hyperlink{chapter_i_topologies_and_sheaves}{Chapter I Topologies and sheaves}\dotfill \pageref*{chapter_i_topologies_and_sheaves} \linebreak \noindent\hyperlink{1_topologies}{1. Topologies}\dotfill \pageref*{1_topologies} \linebreak \noindent\hyperlink{2_abelian_presheaves_on_topologies}{2. Abelian presheaves on topologies}\dotfill \pageref*{2_abelian_presheaves_on_topologies} \linebreak \noindent\hyperlink{21_the_category_of_abelian_presheaves}{2.1 The category of abelian presheaves}\dotfill \pageref*{21_the_category_of_abelian_presheaves} \linebreak \noindent\hyperlink{22_cech_cohomology}{2.2 Cech cohomology}\dotfill \pageref*{22_cech_cohomology} \linebreak \noindent\hyperlink{23_the_functors__and_}{2.3 The functors $f^p$ and $f_p$}\dotfill \pageref*{23_the_functors__and_} \linebreak \noindent\hyperlink{3_abelian_sheaves_on_topologies}{3. Abelian sheaves on topologies}\dotfill \pageref*{3_abelian_sheaves_on_topologies} \linebreak \noindent\hyperlink{31_the_associated_sheaf_of_a_presheaf}{3.1 The associated sheaf of a presheaf}\dotfill \pageref*{31_the_associated_sheaf_of_a_presheaf} \linebreak \noindent\hyperlink{32_the_category_of_abelian_sheaves}{3.2 The category of abelian sheaves}\dotfill \pageref*{32_the_category_of_abelian_sheaves} \linebreak \noindent\hyperlink{33_cohomology_of_abelian_sheaves}{3.3 Cohomology of abelian sheaves}\dotfill \pageref*{33_cohomology_of_abelian_sheaves} \linebreak \noindent\hyperlink{34_the_spectral_sequences_for_cech_cohomology}{3.4 The spectral sequences for Cech cohomology}\dotfill \pageref*{34_the_spectral_sequences_for_cech_cohomology} \linebreak \noindent\hyperlink{35_flabby_sheaves}{3.5 Flabby sheaves}\dotfill \pageref*{35_flabby_sheaves} \linebreak \noindent\hyperlink{36_the_functors__and_}{3.6 The functors $f^s$ and $f_s$}\dotfill \pageref*{36_the_functors__and_} \linebreak \noindent\hyperlink{37_the_leray_spectral_sequence}{3.7 The Leray spectral sequence}\dotfill \pageref*{37_the_leray_spectral_sequence} \linebreak \noindent\hyperlink{38_localization}{3.8 Localization}\dotfill \pageref*{38_localization} \linebreak \noindent\hyperlink{39_the_comparison_lemma}{3.9 The comparison lemma}\dotfill \pageref*{39_the_comparison_lemma} \linebreak \noindent\hyperlink{310_noetherian_topologies}{3.10 Noetherian topologies}\dotfill \pageref*{310_noetherian_topologies} \linebreak \noindent\hyperlink{311_commutation_of_the_functors__with_pseudofiltered_inductive_limits}{3.11 Commutation of the functors $H^q(U,-)$ with pseudofiltered inductive limits}\dotfill \pageref*{311_commutation_of_the_functors__with_pseudofiltered_inductive_limits} \linebreak \noindent\hyperlink{chapter_ii_tale_cohomology}{Chapter II \'E{}tale Cohomology}\dotfill \pageref*{chapter_ii_tale_cohomology} \linebreak \noindent\hyperlink{1_the_tale_site_of_a_scheme}{1. The \'E{}tale site of a scheme}\dotfill \pageref*{1_the_tale_site_of_a_scheme} \linebreak \noindent\hyperlink{11_tale_morphisms}{1.1 \'E{}tale morphisms}\dotfill \pageref*{11_tale_morphisms} \linebreak \noindent\hyperlink{12_tale_site}{1.2 \'E{}tale site}\dotfill \pageref*{12_tale_site} \linebreak \noindent\hyperlink{13_relation_between_tale_and_zariski_cohomology}{1.3 Relation between \'E{}tale and Zariski cohomology}\dotfill \pageref*{13_relation_between_tale_and_zariski_cohomology} \linebreak \noindent\hyperlink{14_the_functors__and_}{1.4 The functors $f_\ast$ and $f^\ast$}\dotfill \pageref*{14_the_functors__and_} \linebreak \noindent\hyperlink{15_the_restricted_tale_site}{1.5 The restricted \'E{}tale site}\dotfill \pageref*{15_the_restricted_tale_site} \linebreak \noindent\hyperlink{2_the_case_}{2. The case $X = Spec(k)$}\dotfill \pageref*{2_the_case_} \linebreak \noindent\hyperlink{3_examples_of_tale_sheaves}{3. Examples of \'e{}tale sheaves}\dotfill \pageref*{3_examples_of_tale_sheaves} \linebreak \noindent\hyperlink{31_representable_sheaves}{3.1 Representable sheaves}\dotfill \pageref*{31_representable_sheaves} \linebreak \noindent\hyperlink{32_tale_sheaves_of_modules}{3.2 \'E{}tale sheaves of $\mathcal{O}_X$-modules}\dotfill \pageref*{32_tale_sheaves_of_modules} \linebreak \noindent\hyperlink{33_big_tale_site}{3.3 Big \'e{}tale site}\dotfill \pageref*{33_big_tale_site} \linebreak \noindent\hyperlink{4_the_theories_of_artinschreier_and_of_kummer}{4. The theories of Artin-Schreier and of Kummer}\dotfill \pageref*{4_the_theories_of_artinschreier_and_of_kummer} \linebreak \noindent\hyperlink{41_the_groups_}{4.1 The groups $H^q(X, (\mathbb{G}_a)_X)$}\dotfill \pageref*{41_the_groups_} \linebreak \noindent\hyperlink{42_the_artinschreier_sequence}{4.2 The Artin-Schreier sequence}\dotfill \pageref*{42_the_artinschreier_sequence} \linebreak \noindent\hyperlink{43_the_groups_}{4.3 The groups $H^q(X, (\mathbb{G}_m)_X)$}\dotfill \pageref*{43_the_groups_} \linebreak \noindent\hyperlink{44_the_kummer_sequence}{4.4 The Kummer sequence}\dotfill \pageref*{44_the_kummer_sequence} \linebreak \noindent\hyperlink{45_the_sheaf_of_divisors_on_}{4.5 The sheaf of divisors on $X_{et}$}\dotfill \pageref*{45_the_sheaf_of_divisors_on_} \linebreak \noindent\hyperlink{5_stalks_of_tale_sheaves}{5. Stalks of \'e{}tale sheaves}\dotfill \pageref*{5_stalks_of_tale_sheaves} \linebreak \noindent\hyperlink{6_strict_localizations}{6. Strict localizations}\dotfill \pageref*{6_strict_localizations} \linebreak \noindent\hyperlink{61_henselian_rings_and_strictly_local_rings}{6.1 Henselian rings and strictly local rings}\dotfill \pageref*{61_henselian_rings_and_strictly_local_rings} \linebreak \noindent\hyperlink{62_strict_localization_of_a_scheme}{6.2 Strict localization of a scheme}\dotfill \pageref*{62_strict_localization_of_a_scheme} \linebreak \noindent\hyperlink{63_tale_cohomology_on_projective_limits_of_schemes}{6.3 \'E{}tale cohomology on projective limits of schemes}\dotfill \pageref*{63_tale_cohomology_on_projective_limits_of_schemes} \linebreak \noindent\hyperlink{7_the_artin_spectral_sequence}{7. The Artin spectral sequence}\dotfill \pageref*{7_the_artin_spectral_sequence} \linebreak \noindent\hyperlink{8_the_decomposition_theorem_relative_cohomology}{8. The decomposition theorem. Relative cohomology}\dotfill \pageref*{8_the_decomposition_theorem_relative_cohomology} \linebreak \noindent\hyperlink{9_torsion_sheaves_locally_constant_sheaves_constructible_sheaves}{9. Torsion sheaves, locally constant sheaves, constructible sheaves}\dotfill \pageref*{9_torsion_sheaves_locally_constant_sheaves_constructible_sheaves} \linebreak \noindent\hyperlink{10_tale_cohomology_of_curves}{10. \'E{}tale cohomology of curves}\dotfill \pageref*{10_tale_cohomology_of_curves} \linebreak \noindent\hyperlink{11_general_theorems_in_tale_cohomology_theory}{11. General theorems in \'e{}tale cohomology theory}\dotfill \pageref*{11_general_theorems_in_tale_cohomology_theory} \linebreak \hypertarget{chapter_0_preliminaries}{}\subsection*{{Chapter 0 Preliminaries}}\label{chapter_0_preliminaries} \hypertarget{1_abelian_categories}{}\subsubsection*{{1. Abelian categories}}\label{1_abelian_categories} \begin{itemize}% \item [[abelian category]] \end{itemize} \hypertarget{2_homological_algebra_in_abelian_categories}{}\subsubsection*{{2. Homological algebra in abelian categories}}\label{2_homological_algebra_in_abelian_categories} \begin{itemize}% \item [[homological algebra]] \end{itemize} \hypertarget{21_functors}{}\paragraph*{{2.1 $\delta$-Functors}}\label{21_functors} \begin{itemize}% \item [[delta-functor]] \end{itemize} \hypertarget{22_derived_functors}{}\paragraph*{{2.2 Derived functors}}\label{22_derived_functors} \begin{itemize}% \item [[derived functor]] \end{itemize} \hypertarget{23_spectral_sequences}{}\paragraph*{{2.3 Spectral sequences}}\label{23_spectral_sequences} \begin{itemize}% \item [[spectral sequence]] \item [[edge morphism]] \item (2.3.5) [[Grothendieck spectral sequence]] \end{itemize} \hypertarget{3_inductive_limits}{}\subsubsection*{{3. Inductive limits}}\label{3_inductive_limits} \hypertarget{chapter_i_topologies_and_sheaves}{}\subsection*{{Chapter I Topologies and sheaves}}\label{chapter_i_topologies_and_sheaves} \hypertarget{1_topologies}{}\subsubsection*{{1. Topologies}}\label{1_topologies} \begin{itemize}% \item [[Grothendieck topology]] \end{itemize} \hypertarget{2_abelian_presheaves_on_topologies}{}\subsubsection*{{2. Abelian presheaves on topologies}}\label{2_abelian_presheaves_on_topologies} \hypertarget{21_the_category_of_abelian_presheaves}{}\paragraph*{{2.1 The category of abelian presheaves}}\label{21_the_category_of_abelian_presheaves} \begin{itemize}% \item [[group object]] \end{itemize} \hypertarget{22_cech_cohomology}{}\paragraph*{{2.2 Cech cohomology}}\label{22_cech_cohomology} \hypertarget{23_the_functors__and_}{}\paragraph*{{2.3 The functors $f^p$ and $f_p$}}\label{23_the_functors__and_} \begin{itemize}% \item [[morphism of sites]] \item [[direct image]], [[inverse image]] (here: on [[presheaves]]) \end{itemize} \hypertarget{3_abelian_sheaves_on_topologies}{}\subsubsection*{{3. Abelian sheaves on topologies}}\label{3_abelian_sheaves_on_topologies} \hypertarget{31_the_associated_sheaf_of_a_presheaf}{}\paragraph*{{3.1 The associated sheaf of a presheaf}}\label{31_the_associated_sheaf_of_a_presheaf} \begin{itemize}% \item [[sheafification]] \end{itemize} \hypertarget{32_the_category_of_abelian_sheaves}{}\paragraph*{{3.2 The category of abelian sheaves}}\label{32_the_category_of_abelian_sheaves} \begin{itemize}% \item [[sheaf of abelian groups]] \end{itemize} \hypertarget{33_cohomology_of_abelian_sheaves}{}\paragraph*{{3.3 Cohomology of abelian sheaves}}\label{33_cohomology_of_abelian_sheaves} \begin{itemize}% \item [[abelian sheaf cohomology]] \end{itemize} \hypertarget{34_the_spectral_sequences_for_cech_cohomology}{}\paragraph*{{3.4 The spectral sequences for Cech cohomology}}\label{34_the_spectral_sequences_for_cech_cohomology} \begin{itemize}% \item [[Cech cohomology]] \end{itemize} \hypertarget{35_flabby_sheaves}{}\paragraph*{{3.5 Flabby sheaves}}\label{35_flabby_sheaves} \begin{itemize}% \item [[flabby sheaf]] \end{itemize} \hypertarget{36_the_functors__and_}{}\paragraph*{{3.6 The functors $f^s$ and $f_s$}}\label{36_the_functors__and_} \begin{itemize}% \item [[morphism of sites]] \item [[direct image]], [[inverse image]] \end{itemize} \hypertarget{37_the_leray_spectral_sequence}{}\paragraph*{{3.7 The Leray spectral sequence}}\label{37_the_leray_spectral_sequence} \begin{itemize}% \item [[Leray spectral sequence]] \end{itemize} \hypertarget{38_localization}{}\paragraph*{{3.8 Localization}}\label{38_localization} \begin{itemize}% \item [[localization]] \end{itemize} \hypertarget{39_the_comparison_lemma}{}\paragraph*{{3.9 The comparison lemma}}\label{39_the_comparison_lemma} \hypertarget{310_noetherian_topologies}{}\paragraph*{{3.10 Noetherian topologies}}\label{310_noetherian_topologies} \hypertarget{311_commutation_of_the_functors__with_pseudofiltered_inductive_limits}{}\paragraph*{{3.11 Commutation of the functors $H^q(U,-)$ with pseudofiltered inductive limits}}\label{311_commutation_of_the_functors__with_pseudofiltered_inductive_limits} \hypertarget{chapter_ii_tale_cohomology}{}\subsection*{{Chapter II \'E{}tale Cohomology}}\label{chapter_ii_tale_cohomology} \hypertarget{1_the_tale_site_of_a_scheme}{}\subsubsection*{{1. The \'E{}tale site of a scheme}}\label{1_the_tale_site_of_a_scheme} \hypertarget{11_tale_morphisms}{}\paragraph*{{1.1 \'E{}tale morphisms}}\label{11_tale_morphisms} \begin{itemize}% \item [[étale morphism]] \end{itemize} \hypertarget{12_tale_site}{}\paragraph*{{1.2 \'E{}tale site}}\label{12_tale_site} \begin{itemize}% \item [[étale site]] \end{itemize} \hypertarget{13_relation_between_tale_and_zariski_cohomology}{}\paragraph*{{1.3 Relation between \'E{}tale and Zariski cohomology}}\label{13_relation_between_tale_and_zariski_cohomology} \begin{itemize}% \item \href{etale+cohomology#RelationZariskiEtaleCohomology}{relation to Zariski cohomology} \end{itemize} \hypertarget{14_the_functors__and_}{}\paragraph*{{1.4 The functors $f_\ast$ and $f^\ast$}}\label{14_the_functors__and_} \begin{itemize}% \item [[direct image]], [[inverse image]] \item [[base change]] \end{itemize} \hypertarget{15_the_restricted_tale_site}{}\paragraph*{{1.5 The restricted \'E{}tale site}}\label{15_the_restricted_tale_site} \hypertarget{2_the_case_}{}\subsubsection*{{2. The case $X = Spec(k)$}}\label{2_the_case_} \begin{itemize}% \item [[Galois group]] \end{itemize} \hypertarget{3_examples_of_tale_sheaves}{}\subsubsection*{{3. Examples of \'e{}tale sheaves}}\label{3_examples_of_tale_sheaves} \hypertarget{31_representable_sheaves}{}\paragraph*{{3.1 Representable sheaves}}\label{31_representable_sheaves} \begin{itemize}% \item [[sheaf]], [[descent]] \item [[étale topos]] \item [[representable presheaf]] \item [[canonical topology]] \item [[additive group]], [[multiplicative group]], [[roots of unity]] \end{itemize} \hypertarget{32_tale_sheaves_of_modules}{}\paragraph*{{3.2 \'E{}tale sheaves of $\mathcal{O}_X$-modules}}\label{32_tale_sheaves_of_modules} \begin{itemize}% \item [[sheaf of coherent modules]] \item [[constructible sheaf]] \end{itemize} \hypertarget{33_big_tale_site}{}\paragraph*{{3.3 Big \'e{}tale site}}\label{33_big_tale_site} \begin{itemize}% \item [[big site]] \end{itemize} \hypertarget{4_the_theories_of_artinschreier_and_of_kummer}{}\subsubsection*{{4. The theories of Artin-Schreier and of Kummer}}\label{4_the_theories_of_artinschreier_and_of_kummer} \hypertarget{41_the_groups_}{}\paragraph*{{4.1 The groups $H^q(X, (\mathbb{G}_a)_X)$}}\label{41_the_groups_} \hypertarget{42_the_artinschreier_sequence}{}\paragraph*{{4.2 The Artin-Schreier sequence}}\label{42_the_artinschreier_sequence} \begin{itemize}% \item [[Frobenius morphism]] \item [[Artin-Schreier sequence]] \end{itemize} \hypertarget{43_the_groups_}{}\paragraph*{{4.3 The groups $H^q(X, (\mathbb{G}_m)_X)$}}\label{43_the_groups_} \begin{itemize}% \item [[Hilbert's theorem 90]] \item [[Azumaya algebra]], [[Brauer group]] \end{itemize} \hypertarget{44_the_kummer_sequence}{}\paragraph*{{4.4 The Kummer sequence}}\label{44_the_kummer_sequence} \begin{itemize}% \item [[Kummer sequence]] \end{itemize} \hypertarget{45_the_sheaf_of_divisors_on_}{}\paragraph*{{4.5 The sheaf of divisors on $X_{et}$}}\label{45_the_sheaf_of_divisors_on_} \hypertarget{5_stalks_of_tale_sheaves}{}\subsubsection*{{5. Stalks of \'e{}tale sheaves}}\label{5_stalks_of_tale_sheaves} \begin{itemize}% \item [[stalk]] \end{itemize} \hypertarget{6_strict_localizations}{}\subsubsection*{{6. Strict localizations}}\label{6_strict_localizations} \hypertarget{61_henselian_rings_and_strictly_local_rings}{}\paragraph*{{6.1 Henselian rings and strictly local rings}}\label{61_henselian_rings_and_strictly_local_rings} \begin{itemize}% \item [[Henselian ring]] \item [[strictly local ring]] \end{itemize} \hypertarget{62_strict_localization_of_a_scheme}{}\subsubsection*{{6.2 Strict localization of a scheme}}\label{62_strict_localization_of_a_scheme} \hypertarget{63_tale_cohomology_on_projective_limits_of_schemes}{}\subsubsection*{{6.3 \'E{}tale cohomology on projective limits of schemes}}\label{63_tale_cohomology_on_projective_limits_of_schemes} \hypertarget{7_the_artin_spectral_sequence}{}\subsubsection*{{7. The Artin spectral sequence}}\label{7_the_artin_spectral_sequence} \begin{itemize}% \item [[Artin spectral sequence]] \end{itemize} \hypertarget{8_the_decomposition_theorem_relative_cohomology}{}\subsubsection*{{8. The decomposition theorem. Relative cohomology}}\label{8_the_decomposition_theorem_relative_cohomology} \hypertarget{9_torsion_sheaves_locally_constant_sheaves_constructible_sheaves}{}\subsubsection*{{9. Torsion sheaves, locally constant sheaves, constructible sheaves}}\label{9_torsion_sheaves_locally_constant_sheaves_constructible_sheaves} \begin{itemize}% \item [[torsion sheaf]] \item [[constructible sheaf]] \end{itemize} \hypertarget{10_tale_cohomology_of_curves}{}\subsubsection*{{10. \'E{}tale cohomology of curves}}\label{10_tale_cohomology_of_curves} \hypertarget{11_general_theorems_in_tale_cohomology_theory}{}\subsubsection*{{11. General theorems in \'e{}tale cohomology theory}}\label{11_general_theorems_in_tale_cohomology_theory} \begin{itemize}% \item [[proper base change theorem]] \end{itemize} category: reference \end{document}