Poincaré Duality Spaces
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− | A ''Poincaré pair'' of dimension $d$ consists of a pair of spaces $(X,\partial X)$ such that there exists a pair $(\mathcal{L},[X])$ in which $\mathcal{L}$ is a bundle of local coefficients on $X$ which is free abelian of rank one and $[X] \in H_d(X,\partial X;\mathcal {L})$ are such that | + | A ''Poincaré pair'' of dimension $d$ consists of a pair of finitely dominated spaces $(X,\partial X)$ such that there exists a pair $(\mathcal{L},[X])$ in which $\mathcal{L}$ is a bundle of local coefficients on $X$ which is free abelian of rank one and $[X] \in H_d(X,\partial X;\mathcal {L})$ are such that |
$$ \cap [X] : H^*(X;\mathcal{B}) \to H_{d-*}(X,\partial X;\mathcal{B} \otimes \mathcal{L})$$ | $$ \cap [X] : H^*(X;\mathcal{B}) \to H_{d-*}(X,\partial X;\mathcal{B} \otimes \mathcal{L})$$ | ||
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is an isomorphism. Here, $\mathcal B$ is allowed to range over all local coefficient bundles on $X$. | is an isomorphism. Here, $\mathcal B$ is allowed to range over all local coefficient bundles on $X$. | ||
− | + | It suffices to check the above condition when $\mathcal{B}$ is local coefficient bundle over $X$ defined by | |
− | condition when $\mathcal{B}$ is local coefficient bundle over $X$ defined by | + | |
$\Bbb Z[\pi]$, with $\pi$ the fundamental groupoid of $X$. | $\Bbb Z[\pi]$, with $\pi$ the fundamental groupoid of $X$. | ||
==Notes== | ==Notes== | ||
− | * If $\partial X = \emptyset$, one says that $X$ is a ''Poincaré duality space.'' (In view of this, perhaps better terminology would be to call $(X,\partial X)$ a Poincaré space with boundary.) | + | * If $\partial X = \emptyset$, one says that $X$ is a ''Poincaré duality space.'' (In view of this, perhaps better terminology would be to call $(X,\partial X)$ a ''Poincaré space with boundary.'') |
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* $\mathcal L$ is called an ''orientation sheaf'' and $[X]$ is called a fundamental class. The pair $(\mathcal L,[X])$ is unique up to unique isomorphism. | * $\mathcal L$ is called an ''orientation sheaf'' and $[X]$ is called a fundamental class. The pair $(\mathcal L,[X])$ is unique up to unique isomorphism. | ||
− | * If $(X,\partial X)$ with respect to $(\mathcal{L},[X])$ a Poincar\'e pair of dimension $d$, then $\partial X$ is | + | * If $(X,\partial X)$ with respect to $(\mathcal{L},[X])$ a Poincar\'e pair of dimension $d$, then $\partial X$ is a Poincaré space of dimension $d-1$ with respect to $(\mathcal {L}_{|\partial X},\partial [X])$, where $\partial: H_d(X;\mathcal{L}) \to H_{d-1}(\partial X;\mathcal{L}_{|\partial X})$ is the boundary homomorphism. |
==Example== | ==Example== | ||
− | A compact (smooth, PL, TOP or homology) manifold $X$ of dimension $d$ is a Poincaré duality | + | A compact (smooth, PL, TOP or homology) manifold $(X,\partial X)$ of dimension $d$ is a Poincaré duality pair of dimension $d$, where $\mathcal L$ is the orientation sheaf of $X$ and $[X]$ is the manifold fundamental class. |
− | and $[X]$ is the manifold fundamental class. | + | |
Revision as of 18:11, 23 March 2011
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1 Introduction
1 Definition
A Poincaré pair of dimension consists of a pair of finitely dominated spaces such that there exists a pair in which is a bundle of local coefficients on which is free abelian of rank one and are such that
and
are isomorphisms.
is an isomorphism. Here, is allowed to range over all local coefficient bundles on .
It suffices to check the above condition when is local coefficient bundle over defined by , with the fundamental groupoid of .
2 Notes
- If , one says that is a Poincaré duality space. (In view of this, perhaps better terminology would be to call a Poincaré space with boundary.)
- is called an orientation sheaf and is called a fundamental class. The pair is unique up to unique isomorphism.
- If with respect to a Poincar\'e pair of dimension , then is a Poincaré space of dimension with respect to , where is the boundary homomorphism.
3 Example
A compact (smooth, PL, TOP or homology) manifold of dimension is a Poincaré duality pair of dimension , where is the orientation sheaf of and is the manifold fundamental class.