Which two of the following space are homeomorphic to each other?












2












$begingroup$


Which two of the following space are homeomorphic to each other?



begin{align}
X_1&={(x,y)in mathbb{R}^2:xy=0}\
X_2&={(x,y)in mathbb{R}^2:xy=1}\
X_3&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=0}\
X_4&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=1}
end{align}



I want to use the contentedness property.



Efforts:



$X_1$ and $X_4$ are not homeomorphic as $X_1$ is connected and nd $X_2$ is disconnected(two connected component)



By same logic $X_1$ and $X_4$ are not homeomorphic.



If I remove the origin from $X_1$, there are 4 components, but if we remove the origin from $X_3$, there are three connected component. So $X_1$ and $X_3$ are not homeomorphic.



Am I going in the right direction?



How to proceed after this.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    $X_4$ is connected.
    $endgroup$
    – Kavi Rama Murthy
    Jan 15 at 9:14










  • $begingroup$
    @KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:16
















2












$begingroup$


Which two of the following space are homeomorphic to each other?



begin{align}
X_1&={(x,y)in mathbb{R}^2:xy=0}\
X_2&={(x,y)in mathbb{R}^2:xy=1}\
X_3&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=0}\
X_4&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=1}
end{align}



I want to use the contentedness property.



Efforts:



$X_1$ and $X_4$ are not homeomorphic as $X_1$ is connected and nd $X_2$ is disconnected(two connected component)



By same logic $X_1$ and $X_4$ are not homeomorphic.



If I remove the origin from $X_1$, there are 4 components, but if we remove the origin from $X_3$, there are three connected component. So $X_1$ and $X_3$ are not homeomorphic.



Am I going in the right direction?



How to proceed after this.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    $X_4$ is connected.
    $endgroup$
    – Kavi Rama Murthy
    Jan 15 at 9:14










  • $begingroup$
    @KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:16














2












2








2





$begingroup$


Which two of the following space are homeomorphic to each other?



begin{align}
X_1&={(x,y)in mathbb{R}^2:xy=0}\
X_2&={(x,y)in mathbb{R}^2:xy=1}\
X_3&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=0}\
X_4&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=1}
end{align}



I want to use the contentedness property.



Efforts:



$X_1$ and $X_4$ are not homeomorphic as $X_1$ is connected and nd $X_2$ is disconnected(two connected component)



By same logic $X_1$ and $X_4$ are not homeomorphic.



If I remove the origin from $X_1$, there are 4 components, but if we remove the origin from $X_3$, there are three connected component. So $X_1$ and $X_3$ are not homeomorphic.



Am I going in the right direction?



How to proceed after this.










share|cite|improve this question











$endgroup$




Which two of the following space are homeomorphic to each other?



begin{align}
X_1&={(x,y)in mathbb{R}^2:xy=0}\
X_2&={(x,y)in mathbb{R}^2:xy=1}\
X_3&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=0}\
X_4&={(x,y)in mathbb{R}^2: x+ygeq 0 text{ and } xy=1}
end{align}



I want to use the contentedness property.



Efforts:



$X_1$ and $X_4$ are not homeomorphic as $X_1$ is connected and nd $X_2$ is disconnected(two connected component)



By same logic $X_1$ and $X_4$ are not homeomorphic.



If I remove the origin from $X_1$, there are 4 components, but if we remove the origin from $X_3$, there are three connected component. So $X_1$ and $X_3$ are not homeomorphic.



Am I going in the right direction?



How to proceed after this.







general-topology continuity






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 15 at 9:29









José Carlos Santos

177k24138248




177k24138248










asked Jan 15 at 9:10









StammeringMathematicianStammeringMathematician

2,8321324




2,8321324








  • 1




    $begingroup$
    $X_4$ is connected.
    $endgroup$
    – Kavi Rama Murthy
    Jan 15 at 9:14










  • $begingroup$
    @KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:16














  • 1




    $begingroup$
    $X_4$ is connected.
    $endgroup$
    – Kavi Rama Murthy
    Jan 15 at 9:14










  • $begingroup$
    @KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:16








1




1




$begingroup$
$X_4$ is connected.
$endgroup$
– Kavi Rama Murthy
Jan 15 at 9:14




$begingroup$
$X_4$ is connected.
$endgroup$
– Kavi Rama Murthy
Jan 15 at 9:14












$begingroup$
@KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
$endgroup$
– StammeringMathematician
Jan 15 at 9:16




$begingroup$
@KaviRamaMurthy By mistake I wrote "connected", I meant homoeomorphic. Sorry
$endgroup$
– StammeringMathematician
Jan 15 at 9:16










2 Answers
2






active

oldest

votes


















3












$begingroup$

Actually, $X_4$ is connected (it's a branch of a hyperbola) and therefore your argument fails. But if you remove $(0,0)$ from $X_1$, then what remains has four connected components. This proved that $X_1$ and $X_4$ are not homeomorphic.



On the other hand, $X_3$ and $X_4$ are homeomorphic. Just consider the map$$begin{array}{ccc}X_4&longrightarrow&X_3\(x,y)&mapsto&begin{cases}(0,y-x)&text{ if }ygeqslant x\(x-y,0)&text{ otherwise.}end{cases}end{array}$$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:17










  • $begingroup$
    I understood what you meant. What do you think about my answer?
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:19










  • $begingroup$
    How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:21










  • $begingroup$
    I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:28










  • $begingroup$
    Thanks for the quick reply.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:29



















2












$begingroup$

Yes you are right. In fact the only two homeomorphic sets are $X_3$ and $X_4$ since $X_4$ can be interpreted as a warped version of $X_3$. $X_3$, $X_4$ and $X_1$ are connected and $X_2$ is not. Therefore $X_2$ is not homeomorphic to any of the others. Also removing origin from $X_1$ leaves us with $4$ distinct parts in $X_1$ while leaving us $2$ distinct parts in $X_3$ and $X_4$. Therefore the only homeomorphic sets are $X_3$ and $X_4$.






share|cite|improve this answer









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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

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    3












    $begingroup$

    Actually, $X_4$ is connected (it's a branch of a hyperbola) and therefore your argument fails. But if you remove $(0,0)$ from $X_1$, then what remains has four connected components. This proved that $X_1$ and $X_4$ are not homeomorphic.



    On the other hand, $X_3$ and $X_4$ are homeomorphic. Just consider the map$$begin{array}{ccc}X_4&longrightarrow&X_3\(x,y)&mapsto&begin{cases}(0,y-x)&text{ if }ygeqslant x\(x-y,0)&text{ otherwise.}end{cases}end{array}$$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:17










    • $begingroup$
      I understood what you meant. What do you think about my answer?
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:19










    • $begingroup$
      How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:21










    • $begingroup$
      I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:28










    • $begingroup$
      Thanks for the quick reply.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:29
















    3












    $begingroup$

    Actually, $X_4$ is connected (it's a branch of a hyperbola) and therefore your argument fails. But if you remove $(0,0)$ from $X_1$, then what remains has four connected components. This proved that $X_1$ and $X_4$ are not homeomorphic.



    On the other hand, $X_3$ and $X_4$ are homeomorphic. Just consider the map$$begin{array}{ccc}X_4&longrightarrow&X_3\(x,y)&mapsto&begin{cases}(0,y-x)&text{ if }ygeqslant x\(x-y,0)&text{ otherwise.}end{cases}end{array}$$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:17










    • $begingroup$
      I understood what you meant. What do you think about my answer?
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:19










    • $begingroup$
      How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:21










    • $begingroup$
      I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:28










    • $begingroup$
      Thanks for the quick reply.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:29














    3












    3








    3





    $begingroup$

    Actually, $X_4$ is connected (it's a branch of a hyperbola) and therefore your argument fails. But if you remove $(0,0)$ from $X_1$, then what remains has four connected components. This proved that $X_1$ and $X_4$ are not homeomorphic.



    On the other hand, $X_3$ and $X_4$ are homeomorphic. Just consider the map$$begin{array}{ccc}X_4&longrightarrow&X_3\(x,y)&mapsto&begin{cases}(0,y-x)&text{ if }ygeqslant x\(x-y,0)&text{ otherwise.}end{cases}end{array}$$






    share|cite|improve this answer











    $endgroup$



    Actually, $X_4$ is connected (it's a branch of a hyperbola) and therefore your argument fails. But if you remove $(0,0)$ from $X_1$, then what remains has four connected components. This proved that $X_1$ and $X_4$ are not homeomorphic.



    On the other hand, $X_3$ and $X_4$ are homeomorphic. Just consider the map$$begin{array}{ccc}X_4&longrightarrow&X_3\(x,y)&mapsto&begin{cases}(0,y-x)&text{ if }ygeqslant x\(x-y,0)&text{ otherwise.}end{cases}end{array}$$







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Jan 15 at 9:26

























    answered Jan 15 at 9:16









    José Carlos SantosJosé Carlos Santos

    177k24138248




    177k24138248












    • $begingroup$
      By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:17










    • $begingroup$
      I understood what you meant. What do you think about my answer?
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:19










    • $begingroup$
      How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:21










    • $begingroup$
      I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:28










    • $begingroup$
      Thanks for the quick reply.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:29


















    • $begingroup$
      By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:17










    • $begingroup$
      I understood what you meant. What do you think about my answer?
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:19










    • $begingroup$
      How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:21










    • $begingroup$
      I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
      $endgroup$
      – José Carlos Santos
      Jan 15 at 9:28










    • $begingroup$
      Thanks for the quick reply.
      $endgroup$
      – StammeringMathematician
      Jan 15 at 9:29
















    $begingroup$
    By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:17




    $begingroup$
    By mistake I wrote "connected", I meant homoeomorphic. Sorry . I have edited the word in the post.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:17












    $begingroup$
    I understood what you meant. What do you think about my answer?
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:19




    $begingroup$
    I understood what you meant. What do you think about my answer?
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:19












    $begingroup$
    How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:21




    $begingroup$
    How $X_3$ and $X_4$ are homeomorphic. Can you give some hint. And in the OP, am I right in deducing that removing the origin from $X_3$ leaves us with three connected component. Thanks
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:21












    $begingroup$
    I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:28




    $begingroup$
    I've added the homeomorphism that I had in mind. And if you remove a point from $X_3$, that will leave you with two connected components.
    $endgroup$
    – José Carlos Santos
    Jan 15 at 9:28












    $begingroup$
    Thanks for the quick reply.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:29




    $begingroup$
    Thanks for the quick reply.
    $endgroup$
    – StammeringMathematician
    Jan 15 at 9:29











    2












    $begingroup$

    Yes you are right. In fact the only two homeomorphic sets are $X_3$ and $X_4$ since $X_4$ can be interpreted as a warped version of $X_3$. $X_3$, $X_4$ and $X_1$ are connected and $X_2$ is not. Therefore $X_2$ is not homeomorphic to any of the others. Also removing origin from $X_1$ leaves us with $4$ distinct parts in $X_1$ while leaving us $2$ distinct parts in $X_3$ and $X_4$. Therefore the only homeomorphic sets are $X_3$ and $X_4$.






    share|cite|improve this answer









    $endgroup$


















      2












      $begingroup$

      Yes you are right. In fact the only two homeomorphic sets are $X_3$ and $X_4$ since $X_4$ can be interpreted as a warped version of $X_3$. $X_3$, $X_4$ and $X_1$ are connected and $X_2$ is not. Therefore $X_2$ is not homeomorphic to any of the others. Also removing origin from $X_1$ leaves us with $4$ distinct parts in $X_1$ while leaving us $2$ distinct parts in $X_3$ and $X_4$. Therefore the only homeomorphic sets are $X_3$ and $X_4$.






      share|cite|improve this answer









      $endgroup$
















        2












        2








        2





        $begingroup$

        Yes you are right. In fact the only two homeomorphic sets are $X_3$ and $X_4$ since $X_4$ can be interpreted as a warped version of $X_3$. $X_3$, $X_4$ and $X_1$ are connected and $X_2$ is not. Therefore $X_2$ is not homeomorphic to any of the others. Also removing origin from $X_1$ leaves us with $4$ distinct parts in $X_1$ while leaving us $2$ distinct parts in $X_3$ and $X_4$. Therefore the only homeomorphic sets are $X_3$ and $X_4$.






        share|cite|improve this answer









        $endgroup$



        Yes you are right. In fact the only two homeomorphic sets are $X_3$ and $X_4$ since $X_4$ can be interpreted as a warped version of $X_3$. $X_3$, $X_4$ and $X_1$ are connected and $X_2$ is not. Therefore $X_2$ is not homeomorphic to any of the others. Also removing origin from $X_1$ leaves us with $4$ distinct parts in $X_1$ while leaving us $2$ distinct parts in $X_3$ and $X_4$. Therefore the only homeomorphic sets are $X_3$ and $X_4$.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 15 at 9:29









        Mostafa AyazMostafa Ayaz

        18.1k31040




        18.1k31040






























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