Comparisons of convenient categories for algebraic topology
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I've heard that there are many convenient categories for algebraic topology. Such categories often have many nice properties like being cartesian closed, complete, cocomplete, the forgetful functor creates limits, containing all "nice" spaces like CW complexes and topological manifolds, et cetera. But the only convenient category for algebraic topologies that I know are the category of compact generated weakly Hausdorff (CGWH) spaces. Can someone briefly summarize other such categories and their advantages and disadvantages when compared to the category of CGWH spaces?
at.algebraic-topology ct.category-theory
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up vote
11
down vote
favorite
I've heard that there are many convenient categories for algebraic topology. Such categories often have many nice properties like being cartesian closed, complete, cocomplete, the forgetful functor creates limits, containing all "nice" spaces like CW complexes and topological manifolds, et cetera. But the only convenient category for algebraic topologies that I know are the category of compact generated weakly Hausdorff (CGWH) spaces. Can someone briefly summarize other such categories and their advantages and disadvantages when compared to the category of CGWH spaces?
at.algebraic-topology ct.category-theory
add a comment |
up vote
11
down vote
favorite
up vote
11
down vote
favorite
I've heard that there are many convenient categories for algebraic topology. Such categories often have many nice properties like being cartesian closed, complete, cocomplete, the forgetful functor creates limits, containing all "nice" spaces like CW complexes and topological manifolds, et cetera. But the only convenient category for algebraic topologies that I know are the category of compact generated weakly Hausdorff (CGWH) spaces. Can someone briefly summarize other such categories and their advantages and disadvantages when compared to the category of CGWH spaces?
at.algebraic-topology ct.category-theory
I've heard that there are many convenient categories for algebraic topology. Such categories often have many nice properties like being cartesian closed, complete, cocomplete, the forgetful functor creates limits, containing all "nice" spaces like CW complexes and topological manifolds, et cetera. But the only convenient category for algebraic topologies that I know are the category of compact generated weakly Hausdorff (CGWH) spaces. Can someone briefly summarize other such categories and their advantages and disadvantages when compared to the category of CGWH spaces?
at.algebraic-topology ct.category-theory
at.algebraic-topology ct.category-theory
edited Dec 6 at 0:42
Goldstern
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11.1k13260
asked Dec 6 at 0:03
Rick Sternbach
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2188
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3 Answers
3
active
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up vote
14
down vote
From the nLab (although I was the author of these words):
A reasonably large class of examples, including the examples of compactly generated spaces and sequential spaces, is given in the article by Escardó, Lawson, and Simpson (ref). These may be outlined as follows. An exponentiable space in $Top$ is a space $X$ such that $X times -: Top to Top$ has a right adjoint. These may be described concretely as core-compact spaces (spaces whose topology is a [[continuous lattice]]). Suppose given a collection $mathcal{C}$ of core-compact spaces, with the property that the product of any two spaces in $mathcal{C}$ is a colimit in $Top$ of spaces in $mathcal{C}$. Such a collection $mathcal{C}$ is called productive. Spaces which are $Top$-colimits of spaces in $mathcal{C}$ are called $mathcal{C}$-generated.
Theorem (Escardó, Lawson, Simpson): If $mathcal{C}$ is a productive class, then the full subcategory of $Top$ whose objects are $mathcal{C}$-generated is a coreflective subcategory of $Top$ (hence complete and cocomplete) that is cartesian closed.
Other convenience conditions, such as inclusion of CW-complexes and closure under closed subspaces, are in practice usually satisfied as well. For example, if closed subspaces of objects of $mathcal{C}$ are $mathcal{C}$-generated, then closed subspaces of $mathcal{C}$-generated spaces are also $mathcal{C}$-generated. If the unit interval $I$ is $mathcal{C}$-generated, then so are all CW-complexes.
A number of examples are scattered throughout the paper.
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
add a comment |
up vote
7
down vote
If you want a convenient category of pointed spaces, then the category $mathbf{NG}_0$ of pointed numerically generated spaces, discussed for instance in
Kazuhisa Shimakawa, Kohei Yoshida, Tadayuki Haraguchi, Homology and cohomology via enriched bifunctors Kyushu Journal of Mathematics, 2018, Volume 72, Issue 2, Pages 239-252, doi:10.2206/kyushujm.72.239
is one. The authors say that numerically generated is equivalent to being $Delta$-generated, as discussed in Dan Dugger's Notes on Delta-generated spaces.
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
add a comment |
up vote
4
down vote
One property that one sometimes wants, but which is not satisfied by most of the "usual" convenient categories, is that of being locally cartesian closed, or equivalently that each pullback functor $f^* : mathcal{C}/Y to mathcal{C}/X$ has a right adjoint $f_*$.
However, I don't know of any nontrivial subcategory of the usual category $mathrm{Top}$ of topological spaces that is locally cartesian closed. The closest locally cartesian closed categories to $mathrm{Top}$ that I know of are quasitoposes, such as the category of subsequential spaces (which contains the category of sequential spaces mentioned by Todd, and is locally presentable) or pseudotopological spaces (which contains the entire category $mathrm{Top}$, but is not locally presentable).
Another approach, used by May and Sigurdsson, is to mix two convenient categories to approximate local cartesian closure. As explained in their book, if $mathcal{K}$ denotes the category of not-necessarily-weak-Hausdorff $k$-spaces, then the pullback functor $f^*:mathcal{K}/Yto mathcal{K}/X$ has a right adjoint as long as $X$ and $Y$ are weak Hausdorff.
add a comment |
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
14
down vote
From the nLab (although I was the author of these words):
A reasonably large class of examples, including the examples of compactly generated spaces and sequential spaces, is given in the article by Escardó, Lawson, and Simpson (ref). These may be outlined as follows. An exponentiable space in $Top$ is a space $X$ such that $X times -: Top to Top$ has a right adjoint. These may be described concretely as core-compact spaces (spaces whose topology is a [[continuous lattice]]). Suppose given a collection $mathcal{C}$ of core-compact spaces, with the property that the product of any two spaces in $mathcal{C}$ is a colimit in $Top$ of spaces in $mathcal{C}$. Such a collection $mathcal{C}$ is called productive. Spaces which are $Top$-colimits of spaces in $mathcal{C}$ are called $mathcal{C}$-generated.
Theorem (Escardó, Lawson, Simpson): If $mathcal{C}$ is a productive class, then the full subcategory of $Top$ whose objects are $mathcal{C}$-generated is a coreflective subcategory of $Top$ (hence complete and cocomplete) that is cartesian closed.
Other convenience conditions, such as inclusion of CW-complexes and closure under closed subspaces, are in practice usually satisfied as well. For example, if closed subspaces of objects of $mathcal{C}$ are $mathcal{C}$-generated, then closed subspaces of $mathcal{C}$-generated spaces are also $mathcal{C}$-generated. If the unit interval $I$ is $mathcal{C}$-generated, then so are all CW-complexes.
A number of examples are scattered throughout the paper.
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
add a comment |
up vote
14
down vote
From the nLab (although I was the author of these words):
A reasonably large class of examples, including the examples of compactly generated spaces and sequential spaces, is given in the article by Escardó, Lawson, and Simpson (ref). These may be outlined as follows. An exponentiable space in $Top$ is a space $X$ such that $X times -: Top to Top$ has a right adjoint. These may be described concretely as core-compact spaces (spaces whose topology is a [[continuous lattice]]). Suppose given a collection $mathcal{C}$ of core-compact spaces, with the property that the product of any two spaces in $mathcal{C}$ is a colimit in $Top$ of spaces in $mathcal{C}$. Such a collection $mathcal{C}$ is called productive. Spaces which are $Top$-colimits of spaces in $mathcal{C}$ are called $mathcal{C}$-generated.
Theorem (Escardó, Lawson, Simpson): If $mathcal{C}$ is a productive class, then the full subcategory of $Top$ whose objects are $mathcal{C}$-generated is a coreflective subcategory of $Top$ (hence complete and cocomplete) that is cartesian closed.
Other convenience conditions, such as inclusion of CW-complexes and closure under closed subspaces, are in practice usually satisfied as well. For example, if closed subspaces of objects of $mathcal{C}$ are $mathcal{C}$-generated, then closed subspaces of $mathcal{C}$-generated spaces are also $mathcal{C}$-generated. If the unit interval $I$ is $mathcal{C}$-generated, then so are all CW-complexes.
A number of examples are scattered throughout the paper.
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
add a comment |
up vote
14
down vote
up vote
14
down vote
From the nLab (although I was the author of these words):
A reasonably large class of examples, including the examples of compactly generated spaces and sequential spaces, is given in the article by Escardó, Lawson, and Simpson (ref). These may be outlined as follows. An exponentiable space in $Top$ is a space $X$ such that $X times -: Top to Top$ has a right adjoint. These may be described concretely as core-compact spaces (spaces whose topology is a [[continuous lattice]]). Suppose given a collection $mathcal{C}$ of core-compact spaces, with the property that the product of any two spaces in $mathcal{C}$ is a colimit in $Top$ of spaces in $mathcal{C}$. Such a collection $mathcal{C}$ is called productive. Spaces which are $Top$-colimits of spaces in $mathcal{C}$ are called $mathcal{C}$-generated.
Theorem (Escardó, Lawson, Simpson): If $mathcal{C}$ is a productive class, then the full subcategory of $Top$ whose objects are $mathcal{C}$-generated is a coreflective subcategory of $Top$ (hence complete and cocomplete) that is cartesian closed.
Other convenience conditions, such as inclusion of CW-complexes and closure under closed subspaces, are in practice usually satisfied as well. For example, if closed subspaces of objects of $mathcal{C}$ are $mathcal{C}$-generated, then closed subspaces of $mathcal{C}$-generated spaces are also $mathcal{C}$-generated. If the unit interval $I$ is $mathcal{C}$-generated, then so are all CW-complexes.
A number of examples are scattered throughout the paper.
From the nLab (although I was the author of these words):
A reasonably large class of examples, including the examples of compactly generated spaces and sequential spaces, is given in the article by Escardó, Lawson, and Simpson (ref). These may be outlined as follows. An exponentiable space in $Top$ is a space $X$ such that $X times -: Top to Top$ has a right adjoint. These may be described concretely as core-compact spaces (spaces whose topology is a [[continuous lattice]]). Suppose given a collection $mathcal{C}$ of core-compact spaces, with the property that the product of any two spaces in $mathcal{C}$ is a colimit in $Top$ of spaces in $mathcal{C}$. Such a collection $mathcal{C}$ is called productive. Spaces which are $Top$-colimits of spaces in $mathcal{C}$ are called $mathcal{C}$-generated.
Theorem (Escardó, Lawson, Simpson): If $mathcal{C}$ is a productive class, then the full subcategory of $Top$ whose objects are $mathcal{C}$-generated is a coreflective subcategory of $Top$ (hence complete and cocomplete) that is cartesian closed.
Other convenience conditions, such as inclusion of CW-complexes and closure under closed subspaces, are in practice usually satisfied as well. For example, if closed subspaces of objects of $mathcal{C}$ are $mathcal{C}$-generated, then closed subspaces of $mathcal{C}$-generated spaces are also $mathcal{C}$-generated. If the unit interval $I$ is $mathcal{C}$-generated, then so are all CW-complexes.
A number of examples are scattered throughout the paper.
answered Dec 6 at 1:07
Todd Trimble♦
43.4k5156257
43.4k5156257
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
add a comment |
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
2
2
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
See also Booth, P.I. and Tillotson, J. Monoidal closed categories and convenient categories of topological spaces Pacific J. Math. {88} (1980) 33--53.
– Ronnie Brown
Dec 6 at 12:39
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
Freely-available pdf link for Booth–Tillotson: msp.org/pjm/1980/88-1/pjm-v88-n1-p03-s.pdf
– David Roberts
2 days ago
add a comment |
up vote
7
down vote
If you want a convenient category of pointed spaces, then the category $mathbf{NG}_0$ of pointed numerically generated spaces, discussed for instance in
Kazuhisa Shimakawa, Kohei Yoshida, Tadayuki Haraguchi, Homology and cohomology via enriched bifunctors Kyushu Journal of Mathematics, 2018, Volume 72, Issue 2, Pages 239-252, doi:10.2206/kyushujm.72.239
is one. The authors say that numerically generated is equivalent to being $Delta$-generated, as discussed in Dan Dugger's Notes on Delta-generated spaces.
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
add a comment |
up vote
7
down vote
If you want a convenient category of pointed spaces, then the category $mathbf{NG}_0$ of pointed numerically generated spaces, discussed for instance in
Kazuhisa Shimakawa, Kohei Yoshida, Tadayuki Haraguchi, Homology and cohomology via enriched bifunctors Kyushu Journal of Mathematics, 2018, Volume 72, Issue 2, Pages 239-252, doi:10.2206/kyushujm.72.239
is one. The authors say that numerically generated is equivalent to being $Delta$-generated, as discussed in Dan Dugger's Notes on Delta-generated spaces.
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
add a comment |
up vote
7
down vote
up vote
7
down vote
If you want a convenient category of pointed spaces, then the category $mathbf{NG}_0$ of pointed numerically generated spaces, discussed for instance in
Kazuhisa Shimakawa, Kohei Yoshida, Tadayuki Haraguchi, Homology and cohomology via enriched bifunctors Kyushu Journal of Mathematics, 2018, Volume 72, Issue 2, Pages 239-252, doi:10.2206/kyushujm.72.239
is one. The authors say that numerically generated is equivalent to being $Delta$-generated, as discussed in Dan Dugger's Notes on Delta-generated spaces.
If you want a convenient category of pointed spaces, then the category $mathbf{NG}_0$ of pointed numerically generated spaces, discussed for instance in
Kazuhisa Shimakawa, Kohei Yoshida, Tadayuki Haraguchi, Homology and cohomology via enriched bifunctors Kyushu Journal of Mathematics, 2018, Volume 72, Issue 2, Pages 239-252, doi:10.2206/kyushujm.72.239
is one. The authors say that numerically generated is equivalent to being $Delta$-generated, as discussed in Dan Dugger's Notes on Delta-generated spaces.
answered Dec 6 at 0:42
David Roberts
16.6k462173
16.6k462173
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
add a comment |
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
An important advantage of $Delta$-generated spaces -- shared with sequential spaces, or any full subcategory of $Top$ which is the colimit-closure of a small subcategory (a la Todd's response) is that they are locally presentable, which simplifies certain infinitary constructions like the small object argument.
– Tim Campion
2 days ago
add a comment |
up vote
4
down vote
One property that one sometimes wants, but which is not satisfied by most of the "usual" convenient categories, is that of being locally cartesian closed, or equivalently that each pullback functor $f^* : mathcal{C}/Y to mathcal{C}/X$ has a right adjoint $f_*$.
However, I don't know of any nontrivial subcategory of the usual category $mathrm{Top}$ of topological spaces that is locally cartesian closed. The closest locally cartesian closed categories to $mathrm{Top}$ that I know of are quasitoposes, such as the category of subsequential spaces (which contains the category of sequential spaces mentioned by Todd, and is locally presentable) or pseudotopological spaces (which contains the entire category $mathrm{Top}$, but is not locally presentable).
Another approach, used by May and Sigurdsson, is to mix two convenient categories to approximate local cartesian closure. As explained in their book, if $mathcal{K}$ denotes the category of not-necessarily-weak-Hausdorff $k$-spaces, then the pullback functor $f^*:mathcal{K}/Yto mathcal{K}/X$ has a right adjoint as long as $X$ and $Y$ are weak Hausdorff.
add a comment |
up vote
4
down vote
One property that one sometimes wants, but which is not satisfied by most of the "usual" convenient categories, is that of being locally cartesian closed, or equivalently that each pullback functor $f^* : mathcal{C}/Y to mathcal{C}/X$ has a right adjoint $f_*$.
However, I don't know of any nontrivial subcategory of the usual category $mathrm{Top}$ of topological spaces that is locally cartesian closed. The closest locally cartesian closed categories to $mathrm{Top}$ that I know of are quasitoposes, such as the category of subsequential spaces (which contains the category of sequential spaces mentioned by Todd, and is locally presentable) or pseudotopological spaces (which contains the entire category $mathrm{Top}$, but is not locally presentable).
Another approach, used by May and Sigurdsson, is to mix two convenient categories to approximate local cartesian closure. As explained in their book, if $mathcal{K}$ denotes the category of not-necessarily-weak-Hausdorff $k$-spaces, then the pullback functor $f^*:mathcal{K}/Yto mathcal{K}/X$ has a right adjoint as long as $X$ and $Y$ are weak Hausdorff.
add a comment |
up vote
4
down vote
up vote
4
down vote
One property that one sometimes wants, but which is not satisfied by most of the "usual" convenient categories, is that of being locally cartesian closed, or equivalently that each pullback functor $f^* : mathcal{C}/Y to mathcal{C}/X$ has a right adjoint $f_*$.
However, I don't know of any nontrivial subcategory of the usual category $mathrm{Top}$ of topological spaces that is locally cartesian closed. The closest locally cartesian closed categories to $mathrm{Top}$ that I know of are quasitoposes, such as the category of subsequential spaces (which contains the category of sequential spaces mentioned by Todd, and is locally presentable) or pseudotopological spaces (which contains the entire category $mathrm{Top}$, but is not locally presentable).
Another approach, used by May and Sigurdsson, is to mix two convenient categories to approximate local cartesian closure. As explained in their book, if $mathcal{K}$ denotes the category of not-necessarily-weak-Hausdorff $k$-spaces, then the pullback functor $f^*:mathcal{K}/Yto mathcal{K}/X$ has a right adjoint as long as $X$ and $Y$ are weak Hausdorff.
One property that one sometimes wants, but which is not satisfied by most of the "usual" convenient categories, is that of being locally cartesian closed, or equivalently that each pullback functor $f^* : mathcal{C}/Y to mathcal{C}/X$ has a right adjoint $f_*$.
However, I don't know of any nontrivial subcategory of the usual category $mathrm{Top}$ of topological spaces that is locally cartesian closed. The closest locally cartesian closed categories to $mathrm{Top}$ that I know of are quasitoposes, such as the category of subsequential spaces (which contains the category of sequential spaces mentioned by Todd, and is locally presentable) or pseudotopological spaces (which contains the entire category $mathrm{Top}$, but is not locally presentable).
Another approach, used by May and Sigurdsson, is to mix two convenient categories to approximate local cartesian closure. As explained in their book, if $mathcal{K}$ denotes the category of not-necessarily-weak-Hausdorff $k$-spaces, then the pullback functor $f^*:mathcal{K}/Yto mathcal{K}/X$ has a right adjoint as long as $X$ and $Y$ are weak Hausdorff.
answered Dec 6 at 17:12
Mike Shulman
35.6k480217
35.6k480217
add a comment |
add a comment |
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