Too much long line
$begingroup$
There is a so-called long line in topology, which is a topological space with a base set $[0,1]times mathbb{R}$ with order topology given by lexicographic order: $(x_{1}, y_{1}) < (x_{2}, y_{2})$ if and only if $x_{1} < x_{2}$ or $x_{1} = x_{2}$ and $y_{1} < y_{2}$. Here are some properties of long line. (Actually, definition of long line in the link is more general than the definition above completely different, and we will use the above definition.)
Now let $L_{1}$ be the above long line. Define long long line $L_{2}$ as a topological space with a base set $[0, 1]times L_{1}$ with order topology is given by lexicographic order as before. We can embed $L_{1}$ in $L_{2}$ as $L_{1} simeq {1/2}times L_{1}hookrightarrow L_{2}$. My question is the following:
(1) Are $L_{1}$ and $L_{2}$ are homeomorphic?
(2) If not, we can also define a $long^{3}$ line $L_{3}$ in similar way, and even $L_{n}$ for any $ngeq 1$. What is a direct limit
$$
L_{omega} = lim_{to}L_{n}?
$$
Is there any interesting property of $L_{omega}$?
(3) If we proceed more, then we can also define $$L_{omega + 1}, L_{omega +2}, dots, L_{2omega}, dots, L_{omega^{2}}, dots, L_{omega^{omega}}, dots, L_{epsilon_{0}}, dots$$
for any given ordinals $alpha$. Are they all different?
I think the most important question is (1). Thanks in advance.
Since the definition of my long line is different from the original one, here's the new version of questions for original definition.
First, we have the classical (original?) long ray $R_{1}$, which is a set $omega_{1} times [0, 1)$ with an order topology via lexicographic order.
Now we can define a long line $L_{1}$ by gluing two long rays $R_{1}$ with respect to their endpoints.
To define $L_{2}$, we define $R_{2}$ by $omega_{1} times R_{1}$ with an order topology (lexicographic order again) and glue two copies. By continuing this process, we can define $L_{alpha}$ for any given ordinal $alpha$ (I hope).
general-topology
$endgroup$
add a comment |
$begingroup$
There is a so-called long line in topology, which is a topological space with a base set $[0,1]times mathbb{R}$ with order topology given by lexicographic order: $(x_{1}, y_{1}) < (x_{2}, y_{2})$ if and only if $x_{1} < x_{2}$ or $x_{1} = x_{2}$ and $y_{1} < y_{2}$. Here are some properties of long line. (Actually, definition of long line in the link is more general than the definition above completely different, and we will use the above definition.)
Now let $L_{1}$ be the above long line. Define long long line $L_{2}$ as a topological space with a base set $[0, 1]times L_{1}$ with order topology is given by lexicographic order as before. We can embed $L_{1}$ in $L_{2}$ as $L_{1} simeq {1/2}times L_{1}hookrightarrow L_{2}$. My question is the following:
(1) Are $L_{1}$ and $L_{2}$ are homeomorphic?
(2) If not, we can also define a $long^{3}$ line $L_{3}$ in similar way, and even $L_{n}$ for any $ngeq 1$. What is a direct limit
$$
L_{omega} = lim_{to}L_{n}?
$$
Is there any interesting property of $L_{omega}$?
(3) If we proceed more, then we can also define $$L_{omega + 1}, L_{omega +2}, dots, L_{2omega}, dots, L_{omega^{2}}, dots, L_{omega^{omega}}, dots, L_{epsilon_{0}}, dots$$
for any given ordinals $alpha$. Are they all different?
I think the most important question is (1). Thanks in advance.
Since the definition of my long line is different from the original one, here's the new version of questions for original definition.
First, we have the classical (original?) long ray $R_{1}$, which is a set $omega_{1} times [0, 1)$ with an order topology via lexicographic order.
Now we can define a long line $L_{1}$ by gluing two long rays $R_{1}$ with respect to their endpoints.
To define $L_{2}$, we define $R_{2}$ by $omega_{1} times R_{1}$ with an order topology (lexicographic order again) and glue two copies. By continuing this process, we can define $L_{alpha}$ for any given ordinal $alpha$ (I hope).
general-topology
$endgroup$
2
$begingroup$
Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
$endgroup$
– Eric Wofsey
Feb 5 at 6:47
$begingroup$
@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
$endgroup$
– Seewoo Lee
Feb 5 at 6:56
$begingroup$
Fwiw, I think your line is actually longer than the standard long line.
$endgroup$
– SolveIt
Feb 5 at 7:02
1
$begingroup$
Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:02
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
$endgroup$
– Seewoo Lee
Feb 5 at 7:10
add a comment |
$begingroup$
There is a so-called long line in topology, which is a topological space with a base set $[0,1]times mathbb{R}$ with order topology given by lexicographic order: $(x_{1}, y_{1}) < (x_{2}, y_{2})$ if and only if $x_{1} < x_{2}$ or $x_{1} = x_{2}$ and $y_{1} < y_{2}$. Here are some properties of long line. (Actually, definition of long line in the link is more general than the definition above completely different, and we will use the above definition.)
Now let $L_{1}$ be the above long line. Define long long line $L_{2}$ as a topological space with a base set $[0, 1]times L_{1}$ with order topology is given by lexicographic order as before. We can embed $L_{1}$ in $L_{2}$ as $L_{1} simeq {1/2}times L_{1}hookrightarrow L_{2}$. My question is the following:
(1) Are $L_{1}$ and $L_{2}$ are homeomorphic?
(2) If not, we can also define a $long^{3}$ line $L_{3}$ in similar way, and even $L_{n}$ for any $ngeq 1$. What is a direct limit
$$
L_{omega} = lim_{to}L_{n}?
$$
Is there any interesting property of $L_{omega}$?
(3) If we proceed more, then we can also define $$L_{omega + 1}, L_{omega +2}, dots, L_{2omega}, dots, L_{omega^{2}}, dots, L_{omega^{omega}}, dots, L_{epsilon_{0}}, dots$$
for any given ordinals $alpha$. Are they all different?
I think the most important question is (1). Thanks in advance.
Since the definition of my long line is different from the original one, here's the new version of questions for original definition.
First, we have the classical (original?) long ray $R_{1}$, which is a set $omega_{1} times [0, 1)$ with an order topology via lexicographic order.
Now we can define a long line $L_{1}$ by gluing two long rays $R_{1}$ with respect to their endpoints.
To define $L_{2}$, we define $R_{2}$ by $omega_{1} times R_{1}$ with an order topology (lexicographic order again) and glue two copies. By continuing this process, we can define $L_{alpha}$ for any given ordinal $alpha$ (I hope).
general-topology
$endgroup$
There is a so-called long line in topology, which is a topological space with a base set $[0,1]times mathbb{R}$ with order topology given by lexicographic order: $(x_{1}, y_{1}) < (x_{2}, y_{2})$ if and only if $x_{1} < x_{2}$ or $x_{1} = x_{2}$ and $y_{1} < y_{2}$. Here are some properties of long line. (Actually, definition of long line in the link is more general than the definition above completely different, and we will use the above definition.)
Now let $L_{1}$ be the above long line. Define long long line $L_{2}$ as a topological space with a base set $[0, 1]times L_{1}$ with order topology is given by lexicographic order as before. We can embed $L_{1}$ in $L_{2}$ as $L_{1} simeq {1/2}times L_{1}hookrightarrow L_{2}$. My question is the following:
(1) Are $L_{1}$ and $L_{2}$ are homeomorphic?
(2) If not, we can also define a $long^{3}$ line $L_{3}$ in similar way, and even $L_{n}$ for any $ngeq 1$. What is a direct limit
$$
L_{omega} = lim_{to}L_{n}?
$$
Is there any interesting property of $L_{omega}$?
(3) If we proceed more, then we can also define $$L_{omega + 1}, L_{omega +2}, dots, L_{2omega}, dots, L_{omega^{2}}, dots, L_{omega^{omega}}, dots, L_{epsilon_{0}}, dots$$
for any given ordinals $alpha$. Are they all different?
I think the most important question is (1). Thanks in advance.
Since the definition of my long line is different from the original one, here's the new version of questions for original definition.
First, we have the classical (original?) long ray $R_{1}$, which is a set $omega_{1} times [0, 1)$ with an order topology via lexicographic order.
Now we can define a long line $L_{1}$ by gluing two long rays $R_{1}$ with respect to their endpoints.
To define $L_{2}$, we define $R_{2}$ by $omega_{1} times R_{1}$ with an order topology (lexicographic order again) and glue two copies. By continuing this process, we can define $L_{alpha}$ for any given ordinal $alpha$ (I hope).
general-topology
general-topology
edited Feb 5 at 8:07
Asaf Karagila♦
304k32432763
304k32432763
asked Feb 5 at 5:40
Seewoo LeeSeewoo Lee
6,870927
6,870927
2
$begingroup$
Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
$endgroup$
– Eric Wofsey
Feb 5 at 6:47
$begingroup$
@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
$endgroup$
– Seewoo Lee
Feb 5 at 6:56
$begingroup$
Fwiw, I think your line is actually longer than the standard long line.
$endgroup$
– SolveIt
Feb 5 at 7:02
1
$begingroup$
Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:02
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
$endgroup$
– Seewoo Lee
Feb 5 at 7:10
add a comment |
2
$begingroup$
Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
$endgroup$
– Eric Wofsey
Feb 5 at 6:47
$begingroup$
@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
$endgroup$
– Seewoo Lee
Feb 5 at 6:56
$begingroup$
Fwiw, I think your line is actually longer than the standard long line.
$endgroup$
– SolveIt
Feb 5 at 7:02
1
$begingroup$
Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:02
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
$endgroup$
– Seewoo Lee
Feb 5 at 7:10
2
2
$begingroup$
Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
$endgroup$
– Eric Wofsey
Feb 5 at 6:47
$begingroup$
Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
$endgroup$
– Eric Wofsey
Feb 5 at 6:47
$begingroup$
@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
$endgroup$
– Seewoo Lee
Feb 5 at 6:56
$begingroup$
@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
$endgroup$
– Seewoo Lee
Feb 5 at 6:56
$begingroup$
Fwiw, I think your line is actually longer than the standard long line.
$endgroup$
– SolveIt
Feb 5 at 7:02
$begingroup$
Fwiw, I think your line is actually longer than the standard long line.
$endgroup$
– SolveIt
Feb 5 at 7:02
1
1
$begingroup$
Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:02
$begingroup$
Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:02
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
$endgroup$
– Seewoo Lee
Feb 5 at 7:10
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
$endgroup$
– Seewoo Lee
Feb 5 at 7:10
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Let me redefine $L_2$ as a product of $omega_1$ and the long line with lexicographical order, which seems more interesting. Note that $L_2$ is isomorphic to $omega_1^2times[0,1)$.
We can prove that both spaces are dense complete linear ordered set under the natural order. Completeness seems not trivial so I should sketch a proof of completeness of $I=mutimes[0,1)$ for a limit ordinal $mu$.
Divide $I$ into sets $I_{alpha}={ langle alpha, rrangle :rin [0,1)}$. Consider a subset $A$ of $I$ which is bounded above, so $A$ is contained in some $[(0,0), (nu,0)]$ for some $nu<mu$.
Consider $B={alphalenu: I_alphacap Aneqvarnothing}$ and take $beta=sup B$. If $betain B$, then finding a supremum of $A$ is reduced to finding a supremum of a set of $[0,1)$. If not, the point $(beta,0)$ will be a supremum of $B$.
(Added in Feb 10, 2019: we need to divide cases once more: because $betain B$ does not guarantee $I_beta$ has a supremum. If $r:=sup I_betain [0,1)$, $langlebeta, rrangle $ is a supremum of $A$. If $r=1$, $langlebeta+1,0rangle $ would be.)
Hence every connected subset of $I$ is an interval (see §24 of Munkres' Topology.) We can see that every compact interval in $L_1$ is separable. However $L_2$ is not.
$endgroup$
add a comment |
$begingroup$
We are dealing with $Stimes mathbb{R}$ with the topology given by the base ${a times I : a in S, I$ : open in $mathbb{R}}$. I claim that such $S_{1} times mathbb{R}$ and another $S_{2} times mathbb{R}$ if and only if $|S_{1}| = |S_{2}|$.
Indeed, consider a (set-theoretical) bjection $h : S_{1} rightarrow S_{2}$, and gather all the homeomorephisms between $a times mathbb{R}$ and $h(a) times mathbb{R}$ for $a in S_{1}$ in order to construct entire homeomorphism.
Definitely, it may disturb the "order" of the components, but it does not matter when you focus on topological properties. If one focuses on the equivalence by order-preserving maps, it becomes entirely different story.
$endgroup$
1
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
add a comment |
$begingroup$
Edit: This answer doesn't apply to OP's question, which uses a nonstandard definition of long line. I had glossed over the definition assuming they would be equivalent. Mea culpa.
I think the answer to 1) is no. The largest ordinal you can embed into the long line is $omega_1$ as per Asaf Karagila's answer in What uncountable ordinals live in the long line? , but you can easily embed larger ordinals in your long long line. Extending this line of thinking, we have a positive answer to 3).
$endgroup$
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
add a comment |
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3 Answers
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3 Answers
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$begingroup$
Let me redefine $L_2$ as a product of $omega_1$ and the long line with lexicographical order, which seems more interesting. Note that $L_2$ is isomorphic to $omega_1^2times[0,1)$.
We can prove that both spaces are dense complete linear ordered set under the natural order. Completeness seems not trivial so I should sketch a proof of completeness of $I=mutimes[0,1)$ for a limit ordinal $mu$.
Divide $I$ into sets $I_{alpha}={ langle alpha, rrangle :rin [0,1)}$. Consider a subset $A$ of $I$ which is bounded above, so $A$ is contained in some $[(0,0), (nu,0)]$ for some $nu<mu$.
Consider $B={alphalenu: I_alphacap Aneqvarnothing}$ and take $beta=sup B$. If $betain B$, then finding a supremum of $A$ is reduced to finding a supremum of a set of $[0,1)$. If not, the point $(beta,0)$ will be a supremum of $B$.
(Added in Feb 10, 2019: we need to divide cases once more: because $betain B$ does not guarantee $I_beta$ has a supremum. If $r:=sup I_betain [0,1)$, $langlebeta, rrangle $ is a supremum of $A$. If $r=1$, $langlebeta+1,0rangle $ would be.)
Hence every connected subset of $I$ is an interval (see §24 of Munkres' Topology.) We can see that every compact interval in $L_1$ is separable. However $L_2$ is not.
$endgroup$
add a comment |
$begingroup$
Let me redefine $L_2$ as a product of $omega_1$ and the long line with lexicographical order, which seems more interesting. Note that $L_2$ is isomorphic to $omega_1^2times[0,1)$.
We can prove that both spaces are dense complete linear ordered set under the natural order. Completeness seems not trivial so I should sketch a proof of completeness of $I=mutimes[0,1)$ for a limit ordinal $mu$.
Divide $I$ into sets $I_{alpha}={ langle alpha, rrangle :rin [0,1)}$. Consider a subset $A$ of $I$ which is bounded above, so $A$ is contained in some $[(0,0), (nu,0)]$ for some $nu<mu$.
Consider $B={alphalenu: I_alphacap Aneqvarnothing}$ and take $beta=sup B$. If $betain B$, then finding a supremum of $A$ is reduced to finding a supremum of a set of $[0,1)$. If not, the point $(beta,0)$ will be a supremum of $B$.
(Added in Feb 10, 2019: we need to divide cases once more: because $betain B$ does not guarantee $I_beta$ has a supremum. If $r:=sup I_betain [0,1)$, $langlebeta, rrangle $ is a supremum of $A$. If $r=1$, $langlebeta+1,0rangle $ would be.)
Hence every connected subset of $I$ is an interval (see §24 of Munkres' Topology.) We can see that every compact interval in $L_1$ is separable. However $L_2$ is not.
$endgroup$
add a comment |
$begingroup$
Let me redefine $L_2$ as a product of $omega_1$ and the long line with lexicographical order, which seems more interesting. Note that $L_2$ is isomorphic to $omega_1^2times[0,1)$.
We can prove that both spaces are dense complete linear ordered set under the natural order. Completeness seems not trivial so I should sketch a proof of completeness of $I=mutimes[0,1)$ for a limit ordinal $mu$.
Divide $I$ into sets $I_{alpha}={ langle alpha, rrangle :rin [0,1)}$. Consider a subset $A$ of $I$ which is bounded above, so $A$ is contained in some $[(0,0), (nu,0)]$ for some $nu<mu$.
Consider $B={alphalenu: I_alphacap Aneqvarnothing}$ and take $beta=sup B$. If $betain B$, then finding a supremum of $A$ is reduced to finding a supremum of a set of $[0,1)$. If not, the point $(beta,0)$ will be a supremum of $B$.
(Added in Feb 10, 2019: we need to divide cases once more: because $betain B$ does not guarantee $I_beta$ has a supremum. If $r:=sup I_betain [0,1)$, $langlebeta, rrangle $ is a supremum of $A$. If $r=1$, $langlebeta+1,0rangle $ would be.)
Hence every connected subset of $I$ is an interval (see §24 of Munkres' Topology.) We can see that every compact interval in $L_1$ is separable. However $L_2$ is not.
$endgroup$
Let me redefine $L_2$ as a product of $omega_1$ and the long line with lexicographical order, which seems more interesting. Note that $L_2$ is isomorphic to $omega_1^2times[0,1)$.
We can prove that both spaces are dense complete linear ordered set under the natural order. Completeness seems not trivial so I should sketch a proof of completeness of $I=mutimes[0,1)$ for a limit ordinal $mu$.
Divide $I$ into sets $I_{alpha}={ langle alpha, rrangle :rin [0,1)}$. Consider a subset $A$ of $I$ which is bounded above, so $A$ is contained in some $[(0,0), (nu,0)]$ for some $nu<mu$.
Consider $B={alphalenu: I_alphacap Aneqvarnothing}$ and take $beta=sup B$. If $betain B$, then finding a supremum of $A$ is reduced to finding a supremum of a set of $[0,1)$. If not, the point $(beta,0)$ will be a supremum of $B$.
(Added in Feb 10, 2019: we need to divide cases once more: because $betain B$ does not guarantee $I_beta$ has a supremum. If $r:=sup I_betain [0,1)$, $langlebeta, rrangle $ is a supremum of $A$. If $r=1$, $langlebeta+1,0rangle $ would be.)
Hence every connected subset of $I$ is an interval (see §24 of Munkres' Topology.) We can see that every compact interval in $L_1$ is separable. However $L_2$ is not.
edited Feb 10 at 2:40
answered Feb 5 at 8:35
Hanul JeonHanul Jeon
17.7k42781
17.7k42781
add a comment |
add a comment |
$begingroup$
We are dealing with $Stimes mathbb{R}$ with the topology given by the base ${a times I : a in S, I$ : open in $mathbb{R}}$. I claim that such $S_{1} times mathbb{R}$ and another $S_{2} times mathbb{R}$ if and only if $|S_{1}| = |S_{2}|$.
Indeed, consider a (set-theoretical) bjection $h : S_{1} rightarrow S_{2}$, and gather all the homeomorephisms between $a times mathbb{R}$ and $h(a) times mathbb{R}$ for $a in S_{1}$ in order to construct entire homeomorphism.
Definitely, it may disturb the "order" of the components, but it does not matter when you focus on topological properties. If one focuses on the equivalence by order-preserving maps, it becomes entirely different story.
$endgroup$
1
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
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– Eric Wofsey
Feb 5 at 7:15
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@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
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– Dk-ium
Feb 5 at 7:20
add a comment |
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We are dealing with $Stimes mathbb{R}$ with the topology given by the base ${a times I : a in S, I$ : open in $mathbb{R}}$. I claim that such $S_{1} times mathbb{R}$ and another $S_{2} times mathbb{R}$ if and only if $|S_{1}| = |S_{2}|$.
Indeed, consider a (set-theoretical) bjection $h : S_{1} rightarrow S_{2}$, and gather all the homeomorephisms between $a times mathbb{R}$ and $h(a) times mathbb{R}$ for $a in S_{1}$ in order to construct entire homeomorphism.
Definitely, it may disturb the "order" of the components, but it does not matter when you focus on topological properties. If one focuses on the equivalence by order-preserving maps, it becomes entirely different story.
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1
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Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
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– Eric Wofsey
Feb 5 at 7:10
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@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
add a comment |
$begingroup$
We are dealing with $Stimes mathbb{R}$ with the topology given by the base ${a times I : a in S, I$ : open in $mathbb{R}}$. I claim that such $S_{1} times mathbb{R}$ and another $S_{2} times mathbb{R}$ if and only if $|S_{1}| = |S_{2}|$.
Indeed, consider a (set-theoretical) bjection $h : S_{1} rightarrow S_{2}$, and gather all the homeomorephisms between $a times mathbb{R}$ and $h(a) times mathbb{R}$ for $a in S_{1}$ in order to construct entire homeomorphism.
Definitely, it may disturb the "order" of the components, but it does not matter when you focus on topological properties. If one focuses on the equivalence by order-preserving maps, it becomes entirely different story.
$endgroup$
We are dealing with $Stimes mathbb{R}$ with the topology given by the base ${a times I : a in S, I$ : open in $mathbb{R}}$. I claim that such $S_{1} times mathbb{R}$ and another $S_{2} times mathbb{R}$ if and only if $|S_{1}| = |S_{2}|$.
Indeed, consider a (set-theoretical) bjection $h : S_{1} rightarrow S_{2}$, and gather all the homeomorephisms between $a times mathbb{R}$ and $h(a) times mathbb{R}$ for $a in S_{1}$ in order to construct entire homeomorphism.
Definitely, it may disturb the "order" of the components, but it does not matter when you focus on topological properties. If one focuses on the equivalence by order-preserving maps, it becomes entirely different story.
edited Feb 5 at 7:22
answered Feb 5 at 7:07
Dk-iumDk-ium
762
762
1
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
add a comment |
1
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
1
1
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
Note that saying each $atimesmathbb{R}$ becomes a component doesn't actually determine the topology; you want to say more specifically that $Stimesmathbb{R}$ is topologized as the disjoint union of the subsets $atimesmathbb{R}$.
$endgroup$
– Eric Wofsey
Feb 5 at 7:10
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
@EricWofsey Yes, precisely! Thanks for your comment, and I will elucidate more!
$endgroup$
– Dk-ium
Feb 5 at 7:11
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
My point wasn't that you have to say $atimesmathbb{R}$ has the usual topology, but that you have to actually specify the entire topology of $Stimesmathbb{R}$. Consider for instance the product topology on $mathbb{Q}timesmathbb{R}$ whose components are $atimesmathbb{R}$ but it is not the disjoint union of its components.
$endgroup$
– Eric Wofsey
Feb 5 at 7:15
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
$begingroup$
@EricWofsey Now I got your point. My intuition was too naive, and there goes another amendment...
$endgroup$
– Dk-ium
Feb 5 at 7:20
add a comment |
$begingroup$
Edit: This answer doesn't apply to OP's question, which uses a nonstandard definition of long line. I had glossed over the definition assuming they would be equivalent. Mea culpa.
I think the answer to 1) is no. The largest ordinal you can embed into the long line is $omega_1$ as per Asaf Karagila's answer in What uncountable ordinals live in the long line? , but you can easily embed larger ordinals in your long long line. Extending this line of thinking, we have a positive answer to 3).
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$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
add a comment |
$begingroup$
Edit: This answer doesn't apply to OP's question, which uses a nonstandard definition of long line. I had glossed over the definition assuming they would be equivalent. Mea culpa.
I think the answer to 1) is no. The largest ordinal you can embed into the long line is $omega_1$ as per Asaf Karagila's answer in What uncountable ordinals live in the long line? , but you can easily embed larger ordinals in your long long line. Extending this line of thinking, we have a positive answer to 3).
$endgroup$
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
add a comment |
$begingroup$
Edit: This answer doesn't apply to OP's question, which uses a nonstandard definition of long line. I had glossed over the definition assuming they would be equivalent. Mea culpa.
I think the answer to 1) is no. The largest ordinal you can embed into the long line is $omega_1$ as per Asaf Karagila's answer in What uncountable ordinals live in the long line? , but you can easily embed larger ordinals in your long long line. Extending this line of thinking, we have a positive answer to 3).
$endgroup$
Edit: This answer doesn't apply to OP's question, which uses a nonstandard definition of long line. I had glossed over the definition assuming they would be equivalent. Mea culpa.
I think the answer to 1) is no. The largest ordinal you can embed into the long line is $omega_1$ as per Asaf Karagila's answer in What uncountable ordinals live in the long line? , but you can easily embed larger ordinals in your long long line. Extending this line of thinking, we have a positive answer to 3).
edited Feb 5 at 7:06
answered Feb 5 at 6:08
SolveItSolveIt
462514
462514
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
add a comment |
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
$begingroup$
And you're right of course. Never mind. I'm just nuking the whole thing and giving up on maths for the day.
$endgroup$
– SolveIt
Feb 5 at 8:25
add a comment |
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Your "long line" is quite different from what is usually called the "long line" so I would suggest using a different name to avoid confusing people.
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– Eric Wofsey
Feb 5 at 6:47
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@EricWofsey I can't think of any good replacement except for long-but-not-that-long-line-you-know...
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– Seewoo Lee
Feb 5 at 6:56
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Fwiw, I think your line is actually longer than the standard long line.
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– SolveIt
Feb 5 at 7:02
1
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Also, do you really mean $[0,1]timesmathbb{R}$? That makes $L_1$ rather boring topologically: it's just the product space $Xtimesmathbb{R}$ where $X$ is $[0,1]$ with the discrete topology. Much more interesting is $[0,1]times[0,1]$ or $[0,1]times[0,1)$.
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– Eric Wofsey
Feb 5 at 7:02
$begingroup$
@EricWofsey I definitely agree, and I think the latter ones are what I had in mind.
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– Seewoo Lee
Feb 5 at 7:10