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... A topological space (X, τ, G) is G -Co-paracompact if each Cocover U = {Uα : α ∈ Λ} of X has an open locally finite refinement U * such that , X \ ∪α∈Λ U * ∉ G where U * = {Vα : α ∈ Λ} and for every Uα ∈ U we can find a Vα ∈ V such that Vα ⊆ Uα. Here refinement need not be a cover. ...
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... Hi everyone, this is Superman, who needed my buddy Batman and his sidekick Robin to help with this week’s homework solutions. For some reason my super body and lightning quick reflexes can’t help me solve topology homework questions–could this be another kryptonite? Corey recalls doing number 3 from ...
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... connected. Therefore there exist U, V ⊆ π −1 (A) such that U, V are open (in π −1 (A)), disjoint and U ∪ V = π −1 (A). Note that if x ∈ U , then the connected component of x (which is equal to xGe ) is contained in U . Indeed, assume that xGe 6⊆ U . Then there is h ∈ xGe such that h 6∈ U . Then, sin ...
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... µ-α-open if A iµ(cµ(iµ(A))). µ-β-open if A cµ(iµ(cµ(A))). µ-r-open [9] if A = iµ(cµ(A)) µ-rα-open [1] if there is a µ-r-open set U such that U A cα(U). Definition 2.2 [1] Let (X, µx) be a generalized topological space and A X. Then A is said to be µ-πrα closed set if cπ(A) U whenever A U and U is µ- ...
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... defined as follows: For A ⊂ X, A? (τ, I) = {x ∈ X|U ∩ A ∈ / I for every open neighbourhood U of x}. A Kuratowski closure operator Cl? (.) for a topology τ ? (τ, I) called the ?-topology, finer than τ is defined by Cl? (A) = A ∪ A? (τ, I) where there is no chance of confusion, A? (I) is denoted by A? ...
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Homework Set #2 Math 440 – Topology Topology by J. Munkres

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Grothendieck topology

In category theory, a branch of mathematics, a Grothendieck topology is a structure on a category C which makes the objects of C act like the open sets of a topological space. A category together with a choice of Grothendieck topology is called a site.Grothendieck topologies axiomatize the notion of an open cover. Using the notion of covering provided by a Grothendieck topology, it becomes possible to define sheaves on a category and their cohomology. This was first done in algebraic geometry and algebraic number theory by Alexander Grothendieck to define the étale cohomology of a scheme. It has been used to define other cohomology theories since then, such as l-adic cohomology, flat cohomology, and crystalline cohomology. While Grothendieck topologies are most often used to define cohomology theories, they have found other applications as well, such as to John Tate's theory of rigid analytic geometry.There is a natural way to associate a site to an ordinary topological space, and Grothendieck's theory is loosely regarded as a generalization of classical topology. Under meager point-set hypotheses, namely sobriety, this is completely accurate—it is possible to recover a sober space from its associated site. However simple examples such as the indiscrete topological space show that not all topological spaces can be expressed using Grothendieck topologies. Conversely, there are Grothendieck topologies which do not come from topological spaces.
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