Subsets of a sigma finite measure are sigma finite measures.

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In Royden's text of real analysis, 2nd edd. There is a statement:
Any measurable set contained in a set of sigma finite measure is itself of sigma finite measure, and the union of a countable collection of sets of sigma finite measure is again of sigma finite measure. How can I prove it using a countable collection of measurable sets?







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    In Royden's text of real analysis, 2nd edd. There is a statement:
    Any measurable set contained in a set of sigma finite measure is itself of sigma finite measure, and the union of a countable collection of sets of sigma finite measure is again of sigma finite measure. How can I prove it using a countable collection of measurable sets?







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      up vote
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      favorite









      up vote
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      down vote

      favorite











      In Royden's text of real analysis, 2nd edd. There is a statement:
      Any measurable set contained in a set of sigma finite measure is itself of sigma finite measure, and the union of a countable collection of sets of sigma finite measure is again of sigma finite measure. How can I prove it using a countable collection of measurable sets?







      share|cite|improve this question














      In Royden's text of real analysis, 2nd edd. There is a statement:
      Any measurable set contained in a set of sigma finite measure is itself of sigma finite measure, and the union of a countable collection of sets of sigma finite measure is again of sigma finite measure. How can I prove it using a countable collection of measurable sets?









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      edited Aug 25 at 7:59









      Taroccoesbrocco

      3,72651433




      3,72651433










      asked Aug 25 at 7:25









      temesgen tilahun

      1




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          Sketches:



          • For the first question, call $X$ the space, $B$ the set and consider $bigcup_ninBbb N A_n=X$ and $B_n=Bcap A_n$.


          • For the second question, any $E_n$ is the union of a sequence $A^k_n_kinBbb N$ such that $mu(A^k_n)<infty$ for all $k$. Consider $B_n=bigcuplimits_1le hle n\ 1le kle n A_h^k$ and prove that $bigcuplimits_ninBbb N B_n=bigcuplimits_ninBbb N E_n$.






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          • Can you provide me full part of the proof?
            – temesgen tilahun
            Sep 3 at 18:37










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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          0
          down vote













          Sketches:



          • For the first question, call $X$ the space, $B$ the set and consider $bigcup_ninBbb N A_n=X$ and $B_n=Bcap A_n$.


          • For the second question, any $E_n$ is the union of a sequence $A^k_n_kinBbb N$ such that $mu(A^k_n)<infty$ for all $k$. Consider $B_n=bigcuplimits_1le hle n\ 1le kle n A_h^k$ and prove that $bigcuplimits_ninBbb N B_n=bigcuplimits_ninBbb N E_n$.






          share|cite|improve this answer






















          • Can you provide me full part of the proof?
            – temesgen tilahun
            Sep 3 at 18:37














          up vote
          0
          down vote













          Sketches:



          • For the first question, call $X$ the space, $B$ the set and consider $bigcup_ninBbb N A_n=X$ and $B_n=Bcap A_n$.


          • For the second question, any $E_n$ is the union of a sequence $A^k_n_kinBbb N$ such that $mu(A^k_n)<infty$ for all $k$. Consider $B_n=bigcuplimits_1le hle n\ 1le kle n A_h^k$ and prove that $bigcuplimits_ninBbb N B_n=bigcuplimits_ninBbb N E_n$.






          share|cite|improve this answer






















          • Can you provide me full part of the proof?
            – temesgen tilahun
            Sep 3 at 18:37












          up vote
          0
          down vote










          up vote
          0
          down vote









          Sketches:



          • For the first question, call $X$ the space, $B$ the set and consider $bigcup_ninBbb N A_n=X$ and $B_n=Bcap A_n$.


          • For the second question, any $E_n$ is the union of a sequence $A^k_n_kinBbb N$ such that $mu(A^k_n)<infty$ for all $k$. Consider $B_n=bigcuplimits_1le hle n\ 1le kle n A_h^k$ and prove that $bigcuplimits_ninBbb N B_n=bigcuplimits_ninBbb N E_n$.






          share|cite|improve this answer














          Sketches:



          • For the first question, call $X$ the space, $B$ the set and consider $bigcup_ninBbb N A_n=X$ and $B_n=Bcap A_n$.


          • For the second question, any $E_n$ is the union of a sequence $A^k_n_kinBbb N$ such that $mu(A^k_n)<infty$ for all $k$. Consider $B_n=bigcuplimits_1le hle n\ 1le kle n A_h^k$ and prove that $bigcuplimits_ninBbb N B_n=bigcuplimits_ninBbb N E_n$.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Aug 25 at 7:42

























          answered Aug 25 at 7:35









          Saucy O'Path

          3,531424




          3,531424











          • Can you provide me full part of the proof?
            – temesgen tilahun
            Sep 3 at 18:37
















          • Can you provide me full part of the proof?
            – temesgen tilahun
            Sep 3 at 18:37















          Can you provide me full part of the proof?
          – temesgen tilahun
          Sep 3 at 18:37




          Can you provide me full part of the proof?
          – temesgen tilahun
          Sep 3 at 18:37

















           

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