Property of set exclusion set.

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Let $T$ have the property that for all sets $A, B in T$ we have that $(Abackslash B) in T$.



How can I prove that $forall A,B in T, Acap B in T$?



I was thinking I should start with both expressions:
$(Abackslash B) in T$.



$(Bbackslash A) in T$.



and show that$ (A cup B)backslash((Abackslash B)cup (B backslash A)=Acap B in T$.



I'm not sure how to show that the final part is in that set. It doesn't say anything about unions.










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    up vote
    7
    down vote

    favorite
    1












    Let $T$ have the property that for all sets $A, B in T$ we have that $(Abackslash B) in T$.



    How can I prove that $forall A,B in T, Acap B in T$?



    I was thinking I should start with both expressions:
    $(Abackslash B) in T$.



    $(Bbackslash A) in T$.



    and show that$ (A cup B)backslash((Abackslash B)cup (B backslash A)=Acap B in T$.



    I'm not sure how to show that the final part is in that set. It doesn't say anything about unions.










    share|cite|improve this question

























      up vote
      7
      down vote

      favorite
      1









      up vote
      7
      down vote

      favorite
      1






      1





      Let $T$ have the property that for all sets $A, B in T$ we have that $(Abackslash B) in T$.



      How can I prove that $forall A,B in T, Acap B in T$?



      I was thinking I should start with both expressions:
      $(Abackslash B) in T$.



      $(Bbackslash A) in T$.



      and show that$ (A cup B)backslash((Abackslash B)cup (B backslash A)=Acap B in T$.



      I'm not sure how to show that the final part is in that set. It doesn't say anything about unions.










      share|cite|improve this question















      Let $T$ have the property that for all sets $A, B in T$ we have that $(Abackslash B) in T$.



      How can I prove that $forall A,B in T, Acap B in T$?



      I was thinking I should start with both expressions:
      $(Abackslash B) in T$.



      $(Bbackslash A) in T$.



      and show that$ (A cup B)backslash((Abackslash B)cup (B backslash A)=Acap B in T$.



      I'm not sure how to show that the final part is in that set. It doesn't say anything about unions.







      elementary-set-theory






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      share|cite|improve this question













      share|cite|improve this question




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      edited Sep 5 at 18:53









      Asaf Karagila♦

      295k32411739




      295k32411739










      asked Sep 5 at 18:43









      WesleyGroupshaveFeelingsToo

      340113




      340113




















          2 Answers
          2






          active

          oldest

          votes

















          up vote
          11
          down vote



          accepted










          Hint: $Acap B=Asetminus (Asetminus B)$






          share|cite|improve this answer
















          • 1




            Hold that thought.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 18:48






          • 2




            Beat me to it! +1
            – Fimpellizieri
            Sep 5 at 18:48










          • I just had to show that these two were equivalent and that did the trick, thanks guys.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 19:34


















          up vote
          8
          down vote













          Write $Acap B = Asetminus(Asetminus B)$.






          share|cite|improve this answer




















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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            11
            down vote



            accepted










            Hint: $Acap B=Asetminus (Asetminus B)$






            share|cite|improve this answer
















            • 1




              Hold that thought.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 18:48






            • 2




              Beat me to it! +1
              – Fimpellizieri
              Sep 5 at 18:48










            • I just had to show that these two were equivalent and that did the trick, thanks guys.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 19:34















            up vote
            11
            down vote



            accepted










            Hint: $Acap B=Asetminus (Asetminus B)$






            share|cite|improve this answer
















            • 1




              Hold that thought.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 18:48






            • 2




              Beat me to it! +1
              – Fimpellizieri
              Sep 5 at 18:48










            • I just had to show that these two were equivalent and that did the trick, thanks guys.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 19:34













            up vote
            11
            down vote



            accepted







            up vote
            11
            down vote



            accepted






            Hint: $Acap B=Asetminus (Asetminus B)$






            share|cite|improve this answer












            Hint: $Acap B=Asetminus (Asetminus B)$







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Sep 5 at 18:47









            b00n heT

            8,95511833




            8,95511833







            • 1




              Hold that thought.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 18:48






            • 2




              Beat me to it! +1
              – Fimpellizieri
              Sep 5 at 18:48










            • I just had to show that these two were equivalent and that did the trick, thanks guys.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 19:34













            • 1




              Hold that thought.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 18:48






            • 2




              Beat me to it! +1
              – Fimpellizieri
              Sep 5 at 18:48










            • I just had to show that these two were equivalent and that did the trick, thanks guys.
              – WesleyGroupshaveFeelingsToo
              Sep 5 at 19:34








            1




            1




            Hold that thought.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 18:48




            Hold that thought.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 18:48




            2




            2




            Beat me to it! +1
            – Fimpellizieri
            Sep 5 at 18:48




            Beat me to it! +1
            – Fimpellizieri
            Sep 5 at 18:48












            I just had to show that these two were equivalent and that did the trick, thanks guys.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 19:34





            I just had to show that these two were equivalent and that did the trick, thanks guys.
            – WesleyGroupshaveFeelingsToo
            Sep 5 at 19:34











            up vote
            8
            down vote













            Write $Acap B = Asetminus(Asetminus B)$.






            share|cite|improve this answer
























              up vote
              8
              down vote













              Write $Acap B = Asetminus(Asetminus B)$.






              share|cite|improve this answer






















                up vote
                8
                down vote










                up vote
                8
                down vote









                Write $Acap B = Asetminus(Asetminus B)$.






                share|cite|improve this answer












                Write $Acap B = Asetminus(Asetminus B)$.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered Sep 5 at 18:48









                Fimpellizieri

                16.9k11836




                16.9k11836



























                     

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