Is the Set of Continuous Functions that are the Sum of Even and Odd Functions Meager?











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Consider $X = mathcal{C}([−1,1])$ with the usual norm $|f|_{infty} = sup_{tin [−1,1]}|f(t)|.$



Define
$$mathcal{A}_{+}={ f in X : f(t)=f(−t) space forall tin [−1,1]},$$
$$mathcal{A}_{−}={ f in X : f(t)=−f(−t) space forall t in [−1,1]}. $$



Is $mathcal{A}_{+} +mathcal{A}_{−} = {f +g : f in mathcal{A}_{+},g in mathcal{A}_{−}}$ meager?





I know this set is dense by the Stone-Weierstrass Theorem. However, that doesn't really help. I also know that if the set is closed, then it is meager, but I have difficulties deciding whether it is closed or not. I know the exponential function is a limit of a sequence of a sum of even and odd functions, however one could define it to be that, in which case it doesn't help.





Any hints on how to get going on this problem, and on whether the set $mathcal{A}_{+}+{A}_{-} $ is closed or not? Thank you in advance.










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    up vote
    1
    down vote

    favorite












    Consider $X = mathcal{C}([−1,1])$ with the usual norm $|f|_{infty} = sup_{tin [−1,1]}|f(t)|.$



    Define
    $$mathcal{A}_{+}={ f in X : f(t)=f(−t) space forall tin [−1,1]},$$
    $$mathcal{A}_{−}={ f in X : f(t)=−f(−t) space forall t in [−1,1]}. $$



    Is $mathcal{A}_{+} +mathcal{A}_{−} = {f +g : f in mathcal{A}_{+},g in mathcal{A}_{−}}$ meager?





    I know this set is dense by the Stone-Weierstrass Theorem. However, that doesn't really help. I also know that if the set is closed, then it is meager, but I have difficulties deciding whether it is closed or not. I know the exponential function is a limit of a sequence of a sum of even and odd functions, however one could define it to be that, in which case it doesn't help.





    Any hints on how to get going on this problem, and on whether the set $mathcal{A}_{+}+{A}_{-} $ is closed or not? Thank you in advance.










    share|cite|improve this question
























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      Consider $X = mathcal{C}([−1,1])$ with the usual norm $|f|_{infty} = sup_{tin [−1,1]}|f(t)|.$



      Define
      $$mathcal{A}_{+}={ f in X : f(t)=f(−t) space forall tin [−1,1]},$$
      $$mathcal{A}_{−}={ f in X : f(t)=−f(−t) space forall t in [−1,1]}. $$



      Is $mathcal{A}_{+} +mathcal{A}_{−} = {f +g : f in mathcal{A}_{+},g in mathcal{A}_{−}}$ meager?





      I know this set is dense by the Stone-Weierstrass Theorem. However, that doesn't really help. I also know that if the set is closed, then it is meager, but I have difficulties deciding whether it is closed or not. I know the exponential function is a limit of a sequence of a sum of even and odd functions, however one could define it to be that, in which case it doesn't help.





      Any hints on how to get going on this problem, and on whether the set $mathcal{A}_{+}+{A}_{-} $ is closed or not? Thank you in advance.










      share|cite|improve this question













      Consider $X = mathcal{C}([−1,1])$ with the usual norm $|f|_{infty} = sup_{tin [−1,1]}|f(t)|.$



      Define
      $$mathcal{A}_{+}={ f in X : f(t)=f(−t) space forall tin [−1,1]},$$
      $$mathcal{A}_{−}={ f in X : f(t)=−f(−t) space forall t in [−1,1]}. $$



      Is $mathcal{A}_{+} +mathcal{A}_{−} = {f +g : f in mathcal{A}_{+},g in mathcal{A}_{−}}$ meager?





      I know this set is dense by the Stone-Weierstrass Theorem. However, that doesn't really help. I also know that if the set is closed, then it is meager, but I have difficulties deciding whether it is closed or not. I know the exponential function is a limit of a sequence of a sum of even and odd functions, however one could define it to be that, in which case it doesn't help.





      Any hints on how to get going on this problem, and on whether the set $mathcal{A}_{+}+{A}_{-} $ is closed or not? Thank you in advance.







      real-analysis general-topology functional-analysis metric-spaces baire-category






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          Note that any function can be written as
          $f(x) = {1 over 2} (f(x) + f(-x)) + {1 over 2} (f(x) - f(-x)) $, so
          $mathcal{A}_{+} +mathcal{A}_{−} = X$, which is not meagre.



          (It is not meagre because $C[-1,1]$ is a complete metric space.)






          share|cite|improve this answer























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            1 Answer
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            active

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            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            4
            down vote



            accepted










            Note that any function can be written as
            $f(x) = {1 over 2} (f(x) + f(-x)) + {1 over 2} (f(x) - f(-x)) $, so
            $mathcal{A}_{+} +mathcal{A}_{−} = X$, which is not meagre.



            (It is not meagre because $C[-1,1]$ is a complete metric space.)






            share|cite|improve this answer



























              up vote
              4
              down vote



              accepted










              Note that any function can be written as
              $f(x) = {1 over 2} (f(x) + f(-x)) + {1 over 2} (f(x) - f(-x)) $, so
              $mathcal{A}_{+} +mathcal{A}_{−} = X$, which is not meagre.



              (It is not meagre because $C[-1,1]$ is a complete metric space.)






              share|cite|improve this answer

























                up vote
                4
                down vote



                accepted







                up vote
                4
                down vote



                accepted






                Note that any function can be written as
                $f(x) = {1 over 2} (f(x) + f(-x)) + {1 over 2} (f(x) - f(-x)) $, so
                $mathcal{A}_{+} +mathcal{A}_{−} = X$, which is not meagre.



                (It is not meagre because $C[-1,1]$ is a complete metric space.)






                share|cite|improve this answer














                Note that any function can be written as
                $f(x) = {1 over 2} (f(x) + f(-x)) + {1 over 2} (f(x) - f(-x)) $, so
                $mathcal{A}_{+} +mathcal{A}_{−} = X$, which is not meagre.



                (It is not meagre because $C[-1,1]$ is a complete metric space.)







                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited 36 mins ago

























                answered 41 mins ago









                copper.hat

                125k558158




                125k558158






























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