What is the best that you can say about a function with given property











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Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
$$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,



$(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?



$(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
Then what is the best that you can say about f without any extra assumption on the hypothesis?



I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
Please help. Thanks in advance.










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    Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
    $$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
    where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,



    $(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?



    $(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
    Then what is the best that you can say about f without any extra assumption on the hypothesis?



    I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
    Please help. Thanks in advance.










    share|cite|improve this question
























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
      $$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
      where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,



      $(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?



      $(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
      Then what is the best that you can say about f without any extra assumption on the hypothesis?



      I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
      Please help. Thanks in advance.










      share|cite|improve this question













      Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
      $$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
      where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,



      $(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?



      $(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
      Then what is the best that you can say about f without any extra assumption on the hypothesis?



      I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
      Please help. Thanks in advance.







      general-topology continuity epsilon-delta uniform-continuity






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      asked Nov 15 at 12:34









      Crazy for maths

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          Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
          ii. says $f$ is continuous on $E$.






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            active

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            up vote
            1
            down vote



            accepted










            Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
            ii. says $f$ is continuous on $E$.






            share|cite|improve this answer

























              up vote
              1
              down vote



              accepted










              Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
              ii. says $f$ is continuous on $E$.






              share|cite|improve this answer























                up vote
                1
                down vote



                accepted







                up vote
                1
                down vote



                accepted






                Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
                ii. says $f$ is continuous on $E$.






                share|cite|improve this answer












                Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
                ii. says $f$ is continuous on $E$.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered Nov 15 at 18:27









                Yu Ding

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