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		<summary type="html">&lt;p&gt;192.35.79.113: /* Clinical significance */&lt;/p&gt;
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		<summary type="html">&lt;p&gt;192.35.35.34: /* In two dimensions */&lt;/p&gt;
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&lt;div&gt;[[File:Penrose-dreieck.svg|thumb|A [[Penrose triangle]] depicts a nontrivial element of the first cohomology of an [[annulus (mathematics)|annulus]] with values in the group of distances from the observer&amp;lt;ref&amp;gt;{{Citation |first=Roger |last=Penrose | |authorlink=Roger Penrose |date=1992 |title=On the Cohomology of Impossible Figures |journal=[[Leonardo (journal)|Leonardo]] |volume=25 |issue=3/4 |pages=245–247 |doi=10.2307/1575844}}. Reprinted from {{Citation |first=Roger |last=Penrose | |authorlink=Roger Penrose |date=1991 |title=On the Cohomology of Impossible Figures / La Cohomologie des Figures Impossibles |journal=Structural Topology |volume=17 |pages=11–16 |url=http://www.iri.upc.edu/people/ros/StructuralTopology/ST17/st17.html |accessdate=January 16, 2014}}&amp;lt;/ref&amp;gt;]]&lt;br /&gt;
&lt;br /&gt;
In [[mathematics]], specifically [[algebraic topology]], &#039;&#039;&#039;Čech cohomology&#039;&#039;&#039; is a [[cohomology]] theory based on the intersection properties of [[open set|open]] [[cover (topology)|covers]] of a [[topological space]].  It is named for the mathematician [[Eduard Čech]].&lt;br /&gt;
&lt;br /&gt;
==Motivation==&lt;br /&gt;
Let &#039;&#039;X&#039;&#039; be a topological space, and let &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; be an open cover of &#039;&#039;X&#039;&#039;.  Define a [[simplicial complex]] &amp;lt;math&amp;gt;N(\mathcal{U})&amp;lt;/math&amp;gt;, called the [[nerve of a covering|nerve]] of the covering, as follows:&lt;br /&gt;
* There is one vertex for each element of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt;.&lt;br /&gt;
* There is one edge for each pair &amp;lt;math&amp;gt;U_1,U_2\in\mathcal{U}&amp;lt;/math&amp;gt; such that &amp;lt;math&amp;gt;U_1 \cap U_2 \ne \emptyset&amp;lt;/math&amp;gt;.&lt;br /&gt;
* In general, there is one &#039;&#039;k&#039;&#039;-simplex for each &#039;&#039;k+1&#039;&#039;-element subset &amp;lt;math&amp;gt;\{U_0,\ldots,U_k\}\,\!&amp;lt;/math&amp;gt; of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; for which &amp;lt;math&amp;gt;U_0\cap\cdots\cap U_k\ne\emptyset\,\!&amp;lt;/math&amp;gt;.&lt;br /&gt;
Geometrically, the nerve &amp;lt;math&amp;gt;N(\mathcal{U})&amp;lt;/math&amp;gt; is essentially a &amp;quot;dual complex&amp;quot; (in the sense of a [[dual graph]], or [[Poincaré duality]]) for the covering &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
The idea of Čech cohomology is that, if we choose a &amp;quot;nice&amp;quot; cover &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; consisting of sufficiently small open sets, the resulting simplicial complex &amp;lt;math&amp;gt;N(\mathcal{U})&amp;lt;/math&amp;gt; should be a good combinatorial model for the space &#039;&#039;X&#039;&#039;.  For such a cover, the Čech cohomology of &#039;&#039;X&#039;&#039; is defined to be the [[simplicial homology|simplicial]] [[cohomology]] of the nerve.&lt;br /&gt;
&lt;br /&gt;
This idea can be formalized by the notion of a [[good cover]], for which every open set and every finite intersection of open sets is [[contractible]].  However, a more general approach is to take the [[direct limit]] of the cohomology groups of the nerve over the system of all possible open covers of &#039;&#039;X&#039;&#039;, ordered by [[Open cover#Refinement|refinement]].  This is the approach adopted below.&lt;br /&gt;
&lt;br /&gt;
==Construction==&lt;br /&gt;
&lt;br /&gt;
Let &amp;lt;math&amp;gt;X&amp;lt;/math&amp;gt; be a [[topological space]], and let &amp;lt;math&amp;gt;\mathcal{F}&amp;lt;/math&amp;gt; be a [[presheaf]] of [[abelian group]]s on &amp;lt;math&amp;gt;X&amp;lt;/math&amp;gt;. Let &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; be an [[open cover]] of &amp;lt;math&amp;gt;X&amp;lt;/math&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
===Simplex===&lt;br /&gt;
A &#039;&#039;q&#039;&#039;-&#039;&#039;&#039;simplex&#039;&#039;&#039; &amp;lt;math&amp;gt;\sigma&amp;lt;/math&amp;gt; of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; is an ordered collection of &amp;lt;math&amp;gt;q+1&amp;lt;/math&amp;gt; sets chosen from &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt;, such that the intersection of all these sets is non-empty. This intersection is called the &#039;&#039;support&#039;&#039; of &amp;lt;math&amp;gt;\sigma&amp;lt;/math&amp;gt; and is denoted &amp;lt;math&amp;gt;|\sigma|&amp;lt;/math&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
Now let &amp;lt;math&amp;gt;\sigma = (U_i)_{i \in \{ 0 , \ldots , q \}}&amp;lt;/math&amp;gt; be such a &#039;&#039;q&#039;&#039;-simplex. The &#039;&#039;j-th partial boundary&#039;&#039; of &amp;lt;math&amp;gt;\sigma&amp;lt;/math&amp;gt; is defined to be the &#039;&#039;q-1&#039;&#039;-simplex obtained by removing the &#039;&#039;j&#039;&#039;-th set from &amp;lt;math&amp;gt;\sigma&amp;lt;/math&amp;gt;, that is: &lt;br /&gt;
:&amp;lt;math&amp;gt;\partial_j \sigma := (U_i)_{i \in \{ 0 , \ldots , q \} \setminus \{j\}}.&amp;lt;/math&amp;gt;&lt;br /&gt;
The &#039;&#039;boundary&#039;&#039; of &amp;lt;math&amp;gt;\sigma&amp;lt;/math&amp;gt; is defined as the alternating sum of the partial boundaries:&lt;br /&gt;
:&amp;lt;math&amp;gt;\partial \sigma := \sum_{j=0}^q (-1)^{j+1} \partial_j \sigma.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
===Cochain===&lt;br /&gt;
A &#039;&#039;q&#039;&#039;-&#039;&#039;&#039;cochain&#039;&#039;&#039; of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; with coefficients in &amp;lt;math&amp;gt;\mathcal{F}&amp;lt;/math&amp;gt; is a map which associates to each &#039;&#039;q&#039;&#039;-simplex &amp;amp;sigma; an element of &amp;lt;math&amp;gt;\mathcal{F}(|\sigma|)&amp;lt;/math&amp;gt; and we denote the set of all &#039;&#039;q&#039;&#039;-cochains of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; with coefficients in &amp;lt;math&amp;gt;\mathcal{F}&amp;lt;/math&amp;gt; by &amp;lt;math&amp;gt;C^q(\mathcal U, \mathcal F)&amp;lt;/math&amp;gt;. &amp;lt;math&amp;gt;C^q(\mathcal U, \mathcal F)&amp;lt;/math&amp;gt; is an abelian group by pointwise addition.&lt;br /&gt;
&lt;br /&gt;
===Differential===&lt;br /&gt;
The cochain groups can be made into a [[cochain complex]] &amp;lt;math&amp;gt;(C^{\textbf{.}}(\mathcal U, \mathcal F), \delta)&amp;lt;/math&amp;gt; by defining the &#039;&#039;&#039;coboundary operator&#039;&#039;&#039; &lt;br /&gt;
&amp;lt;math&amp;gt;\delta_q : C^q(\mathcal U, \mathcal F) \to  C^{q+1}(\mathcal{U},&lt;br /&gt;
 \mathcal{F}) &amp;lt;/math&amp;gt; by&lt;br /&gt;
&lt;br /&gt;
&amp;lt;math&amp;gt; \quad (\delta_q \omega)(\sigma) := \sum_{j=0}^{q+1} (-1)^j \mathrm{res}^{|\partial_j \sigma|}_{|\sigma|} \omega (\partial_j \sigma)&amp;lt;/math&amp;gt;,&lt;br /&gt;
&lt;br /&gt;
where &amp;lt;math&amp;gt;\mathrm{res}^{|\partial_j \sigma|}_{|\sigma|}&amp;lt;/math&amp;gt; is the [[Sheaf (mathematics)|restriction morphism]] {{H:title|Notice that &amp;amp;part;&amp;amp;#11388;σ &amp;amp;#8838; σ, but &amp;amp;#124;σ&amp;amp;#124; &amp;amp;#8838; &amp;amp;#124;&amp;amp;part;&amp;amp;#11388;σ&amp;amp;#124; |from}} &amp;lt;math&amp;gt;\mathcal F(|\partial_j \sigma|)&amp;lt;/math&amp;gt; to &amp;lt;math&amp;gt;\mathcal F(|\sigma|).&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
A calculation shows that &amp;lt;math&amp;gt;\delta_{q+1} \circ \delta_q = 0 &amp;lt;/math&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
The coboundary operator is also sometimes called &lt;br /&gt;
the [[codifferential]].&lt;br /&gt;
&lt;br /&gt;
====Cocycle====&lt;br /&gt;
A &#039;&#039;q&#039;&#039;-cochain is called a &#039;&#039;q&#039;&#039;-cocycle if it is in the kernel of &amp;amp;delta;, hence &amp;lt;math&amp;gt;Z^q(\mathcal{U}, \mathcal{F}) := \ker \left( \delta_q : C^q(\mathcal U, \mathcal F) \to  C^{q+1}(\mathcal{U}, \mathcal{F}) \right)&amp;lt;/math&amp;gt; is the set of all &#039;&#039;q&#039;&#039;-cocycles.&lt;br /&gt;
&lt;br /&gt;
Thus a (q-1)-cochain &#039;&#039;f&#039;&#039; is a cocycle if for all &#039;&#039;q&#039;&#039;-simplices &amp;amp;sigma; the cocycle condition &amp;lt;math&amp;gt;\sum_{j=0}^{q-1} (-1)^j \mathrm{res}^{|\partial_j \sigma|}_{|\sigma|} f (\partial_j \sigma) = 0&amp;lt;/math&amp;gt; holds. In particular, a 1-cochain &#039;&#039;f&#039;&#039; is a 1-cocycle if&lt;br /&gt;
:&amp;lt;math&amp;gt;\forall_{\{A, B, C\} \subset \mathcal{U}}\ U:=A \cap B \cap C,\ f(B \cap C)|_U - f(A \cap C)|_U + f(A \cap B)|_U = 0.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
====Coboundary====&lt;br /&gt;
A &#039;&#039;q&#039;&#039;-cochain is called a &#039;&#039;q&#039;&#039;-coboundary if it is in the image of &#039;&#039;&amp;amp;delta;&#039;&#039; and &amp;lt;math&amp;gt;B^q(\mathcal{U}, \mathcal{F}) := \mathrm{im} \left( \delta_{q-1} : C^{q-1}(\mathcal{U}, \mathcal{F}) \to  C^{q}(\mathcal{U}, \mathcal{F}) \right)&amp;lt;/math&amp;gt; is the set of all &#039;&#039;q&#039;&#039;-coboundaries.&lt;br /&gt;
&lt;br /&gt;
For example, a 1-cochain &#039;&#039;f&#039;&#039; is a 1-coboundary if there exists a 0-cochain &#039;&#039;h&#039;&#039; such that &amp;lt;math&amp;gt;\forall_{\{A, B\} \subset \mathcal{U}}, U:=A \cap B, f(U) = (\delta h)(U) = h(A)|_U - h(B)|_U.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
===Cohomology===&lt;br /&gt;
&lt;br /&gt;
The &#039;&#039;&#039;Čech cohomology&#039;&#039;&#039; of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; with values in &amp;lt;math&amp;gt;\mathcal{F}&amp;lt;/math&amp;gt; is defined to be the cohomology of the cochain complex &amp;lt;math&amp;gt;(C^{\textbf{.}}(\mathcal{U}, \mathcal{F}), \delta)&amp;lt;/math&amp;gt;. Thus the &#039;&#039;q&#039;&#039;th Čech cohomology is given by&lt;br /&gt;
:&amp;lt;math&amp;gt;\check{H}^q(\mathcal{U}, \mathcal{F}) := H^q((C^{\textbf{.}}(\mathcal U, \mathcal F), \delta)) = Z^q(\mathcal{U}, \mathcal{F}) / B^q(\mathcal{U}, \mathcal{F})&amp;lt;/math&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
The Čech cohomology of &#039;&#039;X&#039;&#039; is defined by considering [[Cover (topology)#Refinement|refinement]]s of open covers. If &amp;lt;math&amp;gt;\mathcal{V}&amp;lt;/math&amp;gt; is a refinement of &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; then there is a map in cohomology &amp;lt;math&amp;gt;\check{H}^*(\mathcal U,\mathcal F) \to \check{H}^*(\mathcal V,\mathcal F).&amp;lt;/math&amp;gt;&lt;br /&gt;
The open covers of &#039;&#039;X&#039;&#039; form a [[directed set]] under refinement, so the above map leads to a [[direct system (mathematics)|direct system]] of abelian groups. The &#039;&#039;&#039;Čech cohomology&#039;&#039;&#039; of &#039;&#039;X&#039;&#039; with values in &#039;&#039;F&#039;&#039; is defined as the [[direct limit]] &amp;lt;math&amp;gt;\check{H}(X,\mathcal F) := \varinjlim_{\mathcal U} \check{H}(\mathcal U,\mathcal F)&amp;lt;/math&amp;gt; of this system.&lt;br /&gt;
&lt;br /&gt;
The Čech cohomology of &#039;&#039;X&#039;&#039; with coefficients in a fixed abelian group &#039;&#039;A&#039;&#039;, denoted &amp;lt;math&amp;gt;\check{H}(X;A)&amp;lt;/math&amp;gt;, is defined as &amp;lt;math&amp;gt;\check{H}(X,\mathcal{F}_A)&amp;lt;/math&amp;gt; where &amp;lt;math&amp;gt;\mathcal{F}_A&amp;lt;/math&amp;gt; is the [[constant sheaf]] on &#039;&#039;X&#039;&#039; determined by &#039;&#039;A&#039;&#039;.&lt;br /&gt;
&lt;br /&gt;
A variant of Čech cohomology, called &#039;&#039;&#039;numerable Čech cohomology&#039;&#039;&#039;, is defined as above, except that all open covers considered are required to be &#039;&#039;numerable&#039;&#039;: that is, there is a [[partition of unity]] {ρ&amp;lt;sub&amp;gt;&#039;&#039;i&#039;&#039;&amp;lt;/sub&amp;gt;} such that each support &amp;lt;math&amp;gt;\{x|\rho_i(x)&amp;gt;0\}&amp;lt;/math&amp;gt; is contained in some element of the cover. If &#039;&#039;X&#039;&#039; is [[paracompact]] and [[Hausdorff space|Hausdorff]], then numerable Čech cohomology agrees with  the usual Čech cohomology.&lt;br /&gt;
&lt;br /&gt;
==Relation to other cohomology theories==&lt;br /&gt;
&lt;br /&gt;
If &amp;lt;math&amp;gt;X&amp;lt;/math&amp;gt; is [[homotopy equivalent]] to a [[CW complex]], then the Čech cohomology &amp;lt;math&amp;gt;\check{H}^{*}(X;A)&amp;lt;/math&amp;gt; is [[naturally isomorphic]] to the [[singular homology|singular cohomology]] &amp;lt;math&amp;gt; H^*(X;A) \,&amp;lt;/math&amp;gt;. If &#039;&#039;X&#039;&#039; is a [[differentiable manifold]], then &amp;lt;math&amp;gt;\check{H}^*(X;\mathbb{R})&amp;lt;/math&amp;gt; is also naturally isomorphic to the [[de Rham cohomology]]; the article on de Rham cohomology provides a brief review of this isomorphism. For less well-behaved spaces, Čech cohomology differs from singular cohomology. For example if &#039;&#039;X&#039;&#039; is the [[topologist&#039;s sine curve|closed topologist&#039;s sine curve]], then &amp;lt;math&amp;gt;\check{H}^1(X;\mathbb{Z})=\mathbb{Z},&amp;lt;/math&amp;gt; whereas &amp;lt;math&amp;gt;H^1(X;\mathbb{Z})=0.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
If &#039;&#039;X&#039;&#039; is a differentiable manifold and the cover &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; of &#039;&#039;X&#039;&#039; is a &amp;quot;good cover&amp;quot; (&#039;&#039;i.e.&#039;&#039; all the sets &#039;&#039;U&#039;&#039;&amp;lt;sub&amp;gt;α&amp;lt;/sub&amp;gt; are [[Contractible space|contractible]] to a point, and all finite intersections of sets in &amp;lt;math&amp;gt;\mathcal{U}&amp;lt;/math&amp;gt; are either empty or contractible to a point), then &lt;br /&gt;
&amp;lt;math&amp;gt;\check{H}^{*}(\mathcal U;\mathbb{R})&amp;lt;/math&amp;gt; is isomorphic to the de Rham cohomology.&lt;br /&gt;
&lt;br /&gt;
If &#039;&#039;X&#039;&#039; is compact Hausdorff, then Čech cohomology (with coefficients in a discrete group) is isomorphic to [[Alexander-Spanier cohomology]].&lt;br /&gt;
&lt;br /&gt;
==In algebraic geometry==&lt;br /&gt;
Čech cohomology can be defined more generally for objects in a [[site (mathematics)|site]] &#039;&#039;&#039;C&#039;&#039;&#039; endowed with a topology. This applies, for example, to the Zariski site or the etale site of a [[scheme (mathematics)|scheme]] &#039;&#039;X&#039;&#039;. The Čech cohomology with values in some [[sheaf (mathematics)|sheaf]] &#039;&#039;F&#039;&#039; is defined as&lt;br /&gt;
:&amp;lt;math&amp;gt;\check H^n (X, F) := \varinjlim_{\mathcal U} \check H^n(\mathcal U, F).&amp;lt;/math&amp;gt;&lt;br /&gt;
where the [[colimit]] runs over all coverings (with respect to the chosen topology) of &#039;&#039;X&#039;&#039;. Here &amp;lt;math&amp;gt;\check H^n(\mathcal U, F)&amp;lt;/math&amp;gt; is defined as above, except that the &#039;&#039;r&#039;&#039;-fold intersections of open subsets inside the ambient topological space are replaced by the &#039;&#039;r&#039;&#039;-fold [[fiber product]]&lt;br /&gt;
:&amp;lt;math&amp;gt;\mathcal U^{\times^r_X} := \mathcal U \times_X \dots \times_X  \mathcal U.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
As in the classical situation of topological spaces, there is always a map&lt;br /&gt;
:&amp;lt;math&amp;gt;H^n(X, F) \rightarrow \check H^n(X, F)&amp;lt;/math&amp;gt;&lt;br /&gt;
from [[sheaf cohomology]] to Čech cohomology. It is always an isomorphism in degrees &#039;&#039;n&#039;&#039; = 0 and 1, but may fail to be so in general. For the [[Zariski topology]] on a [[Noetherian topological space|Noetherian]] [[separated scheme]], Čech and sheaf cohomology agree for any [[quasi-coherent sheaf]]. For the [[etale topology]], the two cohomologies agree for any sheaf, provided that any finite set of points in the base scheme &#039;&#039;X&#039;&#039; are contained in some open affine subscheme. This is satisfied, for example, if &#039;&#039;X&#039;&#039; is [[quasi-projective variety|quasi-projective]] over an [[affine scheme]].&amp;lt;ref&amp;gt;{{Citation | last1=Milne | first1=James S. | title=Étale cohomology | url=http://books.google.com/books?isbn=978-0-691-08238-7 | publisher=[[Princeton University Press]] | series=Princeton Mathematical Series | isbn=978-0-691-08238-7 | id={{MR|559531}} | year=1980 | volume=33}}, section III.2&amp;lt;/ref&amp;gt;&lt;br /&gt;
&lt;br /&gt;
The possible difference between Cech cohomology and sheaf cohomology is a motivation for the use of [[hypercovering]]s: these are more general objects than the Cech [[nerve (category theory)|nerve]]&lt;br /&gt;
:&amp;lt;math&amp;gt;N_X \mathcal U : \dots \rightarrow \mathcal U \times_X \mathcal U \times_X \mathcal U \rightarrow \mathcal U \times_X \mathcal U \rightarrow \mathcal U.&amp;lt;/math&amp;gt;&lt;br /&gt;
A hypercovering &#039;&#039;K&#039;&#039;&amp;lt;sub&amp;gt;&amp;amp;lowast;&amp;lt;/sub&amp;gt; of &#039;&#039;X&#039;&#039; is a [[simplicial object]] in &#039;&#039;&#039;C&#039;&#039;&#039;, i.e., a collection of objects &#039;&#039;K&#039;&#039;&amp;lt;sub&amp;gt;&#039;&#039;n&#039;&#039;&amp;lt;/sub&amp;gt; together with boundary and degeneracy maps. Applying a sheaf &#039;&#039;F&#039;&#039; to &#039;&#039;K&#039;&#039;&amp;lt;sub&amp;gt;&amp;amp;lowast;&amp;lt;/sub&amp;gt; yields a [[simplicial abelian group]] &#039;&#039;F&#039;&#039;(&#039;&#039;K&#039;&#039;&amp;lt;sub&amp;gt;&amp;amp;lowast;&amp;lt;/sub&amp;gt;) whose &#039;&#039;n&#039;&#039;-th cohomology group is denoted &#039;&#039;H&#039;&#039;&amp;lt;sup&amp;gt;&#039;&#039;n&#039;&#039;&amp;lt;/sup&amp;gt;(&#039;&#039;F&#039;&#039;(&#039;&#039;K&#039;&#039;&amp;lt;sub&amp;gt;&amp;amp;lowast;&amp;lt;/sub&amp;gt;)). (This group is the same as &amp;lt;math&amp;gt;\check H^n(\mathcal U, F)&amp;lt;/math&amp;gt; in case &#039;&#039;K&#039;&#039; equals &amp;lt;math&amp;gt;N_X \mathcal U &amp;lt;/math&amp;gt;.) Then, it can be shown that there is a canonical isomorphism&lt;br /&gt;
:&amp;lt;math&amp;gt;H^n (X, F) = \varinjlim_{K_*} H^n(F(K_*)),&amp;lt;/math&amp;gt;&lt;br /&gt;
where the colimit now runs over all hypercoverings.&amp;lt;ref&amp;gt;{{Citation | last1=Artin | first1=Michael | author1-link=Michael Artin | last2=Mazur | first2=Barry | author2-link=Barry Mazur | title=Etale homotopy | publisher=[[Springer-Verlag]] | location=Berlin, New York | series=Lecture Notes in Mathematics, No. 100 | year=1969}}, Theorem 8.16&amp;lt;/ref&amp;gt;&lt;br /&gt;
&lt;br /&gt;
==References==&lt;br /&gt;
&amp;lt;references /&amp;gt;&lt;br /&gt;
&lt;br /&gt;
*{{cite book | last = Bott | first = Raoul | authorlink = Raoul Bott | coauthors = Loring Tu | title = Differential Forms in Algebraic Topology | year = 1982 | publisher = Springer | location = New York | isbn = 0-387-90613-4}}&lt;br /&gt;
*{{cite book | last = Hatcher | first = Allen | authorlink = Allen Hatcher | year = 2002 | title = Algebraic Topology | publisher = Cambridge University Press | isbn = 0-521-79540-0 | url = http://www.math.cornell.edu/~hatcher/AT/ATpage.html}} &lt;br /&gt;
*{{cite book | last = Wells | first = Raymond | authorlink = Raymond O&#039;Neil Wells, Jr. | year = 1980 | title = Differential Analysis on Complex Manifolds | publisher = Springer-Verlag}} ISBN 0-387-90419-0. ISBN 3-540-90419-0. Chapter 2 Appendix A&lt;br /&gt;
&lt;br /&gt;
{{DEFAULTSORT:Cech cohomology}}&lt;br /&gt;
[[Category:Algebraic topology]]&lt;br /&gt;
[[Category:Cohomology theories]]&lt;br /&gt;
[[Category:Homology theory]]&lt;/div&gt;</summary>
		<author><name>192.35.35.34</name></author>
	</entry>
	<entry>
		<id>https://en.formulasearchengine.com/w/index.php?title=Jeffreys_prior&amp;diff=240441</id>
		<title>Jeffreys prior</title>
		<link rel="alternate" type="text/html" href="https://en.formulasearchengine.com/w/index.php?title=Jeffreys_prior&amp;diff=240441"/>
		<updated>2012-08-24T14:42:05Z</updated>

		<summary type="html">&lt;p&gt;192.35.44.24: /* One-parameter case */ be more specific about why the derivation follows&lt;/p&gt;
&lt;hr /&gt;
&lt;div&gt;== shortage Kam Lord ==&lt;br /&gt;
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== and one still make fun of them ==&lt;br /&gt;
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		<author><name>192.35.44.24</name></author>
	</entry>
	<entry>
		<id>https://en.formulasearchengine.com/w/index.php?title=Rogowski_coil&amp;diff=226718</id>
		<title>Rogowski coil</title>
		<link rel="alternate" type="text/html" href="https://en.formulasearchengine.com/w/index.php?title=Rogowski_coil&amp;diff=226718"/>
		<updated>2012-08-23T09:49:42Z</updated>

		<summary type="html">&lt;p&gt;192.35.17.30: /* Formulae */&lt;/p&gt;
&lt;hr /&gt;
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		<author><name>192.35.17.30</name></author>
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	<entry>
		<id>https://en.formulasearchengine.com/w/index.php?title=Creation_and_annihilation_operators&amp;diff=233669</id>
		<title>Creation and annihilation operators</title>
		<link rel="alternate" type="text/html" href="https://en.formulasearchengine.com/w/index.php?title=Creation_and_annihilation_operators&amp;diff=233669"/>
		<updated>2012-05-18T21:46:42Z</updated>

		<summary type="html">&lt;p&gt;192.35.35.34: /* Derivation for quantum harmonic oscillator */   The signs in the expressions for the Hamiltonian using operators (aa^+) and (a^+a) were interchanged and are now correct.  Refer to the Wikipedia page on &amp;quot;Quantization_of_the_electromagnetic_field&amp;quot;.&lt;/p&gt;
&lt;hr /&gt;
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		<author><name>192.35.35.34</name></author>
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