Finding a sequence of sets whose limit is a given set [closed]











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Suppose $B$ is a ball in $mathbb{R}^{n}$ with $n>1$, and $F$ a closed set with empty interior. Is there an increasing sequence of sets $E_{1}subset,...E_{n}subset E_{n+1},...$, all Borel sets, such that each $E_{n}subset Bsetminus F$ but $cup_{n}E_{n}=B$?










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closed as unclear what you're asking by Kavi Rama Murthy, user90369, user10354138, Shailesh, Cesareo Nov 20 at 1:15


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.











  • 4




    Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
    – Lord Shark the Unknown
    Nov 19 at 5:32










  • $F$ is a part of $B$ and so their intersection is not empty.
    – M. Rahmat
    Nov 19 at 6:16















up vote
1
down vote

favorite












Suppose $B$ is a ball in $mathbb{R}^{n}$ with $n>1$, and $F$ a closed set with empty interior. Is there an increasing sequence of sets $E_{1}subset,...E_{n}subset E_{n+1},...$, all Borel sets, such that each $E_{n}subset Bsetminus F$ but $cup_{n}E_{n}=B$?










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closed as unclear what you're asking by Kavi Rama Murthy, user90369, user10354138, Shailesh, Cesareo Nov 20 at 1:15


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.











  • 4




    Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
    – Lord Shark the Unknown
    Nov 19 at 5:32










  • $F$ is a part of $B$ and so their intersection is not empty.
    – M. Rahmat
    Nov 19 at 6:16













up vote
1
down vote

favorite









up vote
1
down vote

favorite











Suppose $B$ is a ball in $mathbb{R}^{n}$ with $n>1$, and $F$ a closed set with empty interior. Is there an increasing sequence of sets $E_{1}subset,...E_{n}subset E_{n+1},...$, all Borel sets, such that each $E_{n}subset Bsetminus F$ but $cup_{n}E_{n}=B$?










share|cite|improve this question













Suppose $B$ is a ball in $mathbb{R}^{n}$ with $n>1$, and $F$ a closed set with empty interior. Is there an increasing sequence of sets $E_{1}subset,...E_{n}subset E_{n+1},...$, all Borel sets, such that each $E_{n}subset Bsetminus F$ but $cup_{n}E_{n}=B$?







real-analysis measure-theory elementary-set-theory






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asked Nov 19 at 5:29









M. Rahmat

291211




291211




closed as unclear what you're asking by Kavi Rama Murthy, user90369, user10354138, Shailesh, Cesareo Nov 20 at 1:15


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.






closed as unclear what you're asking by Kavi Rama Murthy, user90369, user10354138, Shailesh, Cesareo Nov 20 at 1:15


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.










  • 4




    Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
    – Lord Shark the Unknown
    Nov 19 at 5:32










  • $F$ is a part of $B$ and so their intersection is not empty.
    – M. Rahmat
    Nov 19 at 6:16














  • 4




    Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
    – Lord Shark the Unknown
    Nov 19 at 5:32










  • $F$ is a part of $B$ and so their intersection is not empty.
    – M. Rahmat
    Nov 19 at 6:16








4




4




Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
– Lord Shark the Unknown
Nov 19 at 5:32




Not if $Bcap F$ is nonempty. Is this actually the question you wished to ask?
– Lord Shark the Unknown
Nov 19 at 5:32












$F$ is a part of $B$ and so their intersection is not empty.
– M. Rahmat
Nov 19 at 6:16




$F$ is a part of $B$ and so their intersection is not empty.
– M. Rahmat
Nov 19 at 6:16










1 Answer
1






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accepted










No.



In general if $A_alpha$ are subsets of a set $D$, then $bigcup_{alpha} A_alpha$ is also a subset of $D$, since any element of the union is an element of some $A_alpha$ and hence an element of $D$.



Thus as Lord Shark the Unknown points out in the comments, if $Bcap F$ is nonempty then $Bsetminus F$ is a proper subset of $B$, so since each $E_n$ is a subset of $Bsetminus F$, we have that $bigcup_n E_n subseteq Bsetminus F subsetneq B$.






share|cite|improve this answer




























    1 Answer
    1






    active

    oldest

    votes








    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes








    up vote
    0
    down vote



    accepted










    No.



    In general if $A_alpha$ are subsets of a set $D$, then $bigcup_{alpha} A_alpha$ is also a subset of $D$, since any element of the union is an element of some $A_alpha$ and hence an element of $D$.



    Thus as Lord Shark the Unknown points out in the comments, if $Bcap F$ is nonempty then $Bsetminus F$ is a proper subset of $B$, so since each $E_n$ is a subset of $Bsetminus F$, we have that $bigcup_n E_n subseteq Bsetminus F subsetneq B$.






    share|cite|improve this answer

























      up vote
      0
      down vote



      accepted










      No.



      In general if $A_alpha$ are subsets of a set $D$, then $bigcup_{alpha} A_alpha$ is also a subset of $D$, since any element of the union is an element of some $A_alpha$ and hence an element of $D$.



      Thus as Lord Shark the Unknown points out in the comments, if $Bcap F$ is nonempty then $Bsetminus F$ is a proper subset of $B$, so since each $E_n$ is a subset of $Bsetminus F$, we have that $bigcup_n E_n subseteq Bsetminus F subsetneq B$.






      share|cite|improve this answer























        up vote
        0
        down vote



        accepted







        up vote
        0
        down vote



        accepted






        No.



        In general if $A_alpha$ are subsets of a set $D$, then $bigcup_{alpha} A_alpha$ is also a subset of $D$, since any element of the union is an element of some $A_alpha$ and hence an element of $D$.



        Thus as Lord Shark the Unknown points out in the comments, if $Bcap F$ is nonempty then $Bsetminus F$ is a proper subset of $B$, so since each $E_n$ is a subset of $Bsetminus F$, we have that $bigcup_n E_n subseteq Bsetminus F subsetneq B$.






        share|cite|improve this answer












        No.



        In general if $A_alpha$ are subsets of a set $D$, then $bigcup_{alpha} A_alpha$ is also a subset of $D$, since any element of the union is an element of some $A_alpha$ and hence an element of $D$.



        Thus as Lord Shark the Unknown points out in the comments, if $Bcap F$ is nonempty then $Bsetminus F$ is a proper subset of $B$, so since each $E_n$ is a subset of $Bsetminus F$, we have that $bigcup_n E_n subseteq Bsetminus F subsetneq B$.







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        answered Nov 20 at 0:53









        jgon

        11.1k11839




        11.1k11839















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