Too much long line












12












$begingroup$


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).










share|cite|improve this question











$endgroup$








  • 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
















12












$begingroup$


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).










share|cite|improve this question











$endgroup$








  • 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














12












12








12


2



$begingroup$


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).










share|cite|improve this question











$endgroup$




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






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








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














  • 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










3 Answers
3






active

oldest

votes


















5












$begingroup$

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.






share|cite|improve this answer











$endgroup$





















    3












    $begingroup$

    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.






    share|cite|improve this answer











    $endgroup$









    • 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



















    1












    $begingroup$

    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).






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      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











    Your Answer





    StackExchange.ifUsing("editor", function () {
    return StackExchange.using("mathjaxEditing", function () {
    StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
    StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
    });
    });
    }, "mathjax-editing");

    StackExchange.ready(function() {
    var channelOptions = {
    tags: "".split(" "),
    id: "69"
    };
    initTagRenderer("".split(" "), "".split(" "), channelOptions);

    StackExchange.using("externalEditor", function() {
    // Have to fire editor after snippets, if snippets enabled
    if (StackExchange.settings.snippets.snippetsEnabled) {
    StackExchange.using("snippets", function() {
    createEditor();
    });
    }
    else {
    createEditor();
    }
    });

    function createEditor() {
    StackExchange.prepareEditor({
    heartbeatType: 'answer',
    autoActivateHeartbeat: false,
    convertImagesToLinks: true,
    noModals: true,
    showLowRepImageUploadWarning: true,
    reputationToPostImages: 10,
    bindNavPrevention: true,
    postfix: "",
    imageUploader: {
    brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
    contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
    allowUrls: true
    },
    noCode: true, onDemand: true,
    discardSelector: ".discard-answer"
    ,immediatelyShowMarkdownHelp:true
    });


    }
    });














    draft saved

    draft discarded


















    StackExchange.ready(
    function () {
    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3100829%2ftoo-much-long-line%23new-answer', 'question_page');
    }
    );

    Post as a guest















    Required, but never shown

























    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    5












    $begingroup$

    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.






    share|cite|improve this answer











    $endgroup$


















      5












      $begingroup$

      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.






      share|cite|improve this answer











      $endgroup$
















        5












        5








        5





        $begingroup$

        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.






        share|cite|improve this answer











        $endgroup$



        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.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Feb 10 at 2:40

























        answered Feb 5 at 8:35









        Hanul JeonHanul Jeon

        17.7k42781




        17.7k42781























            3












            $begingroup$

            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.






            share|cite|improve this answer











            $endgroup$









            • 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
















            3












            $begingroup$

            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.






            share|cite|improve this answer











            $endgroup$









            • 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














            3












            3








            3





            $begingroup$

            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.






            share|cite|improve this answer











            $endgroup$



            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.







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            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














            • 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











            1












            $begingroup$

            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).






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              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
















            1












            $begingroup$

            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).






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              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














            1












            1








            1





            $begingroup$

            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).






            share|cite|improve this answer











            $endgroup$



            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).







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            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


















            • $begingroup$
              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


















            draft saved

            draft discarded




















































            Thanks for contributing an answer to Mathematics Stack Exchange!


            • Please be sure to answer the question. Provide details and share your research!

            But avoid



            • Asking for help, clarification, or responding to other answers.

            • Making statements based on opinion; back them up with references or personal experience.


            Use MathJax to format equations. MathJax reference.


            To learn more, see our tips on writing great answers.




            draft saved


            draft discarded














            StackExchange.ready(
            function () {
            StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3100829%2ftoo-much-long-line%23new-answer', 'question_page');
            }
            );

            Post as a guest















            Required, but never shown





















































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown

































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown







            Popular posts from this blog

            How to change which sound is reproduced for terminal bell?

            Title Spacing in Bjornstrup Chapter, Removing Chapter Number From Contents

            Can I use Tabulator js library in my java Spring + Thymeleaf project?