Every subset equal to original set?












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Is there any set whose every subset is equal to the set itself? It seems like this isn't possible, but maybe something similar is possible.










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    3












    $begingroup$


    Is there any set whose every subset is equal to the set itself? It seems like this isn't possible, but maybe something similar is possible.










    share|cite|improve this question









    $endgroup$















      3












      3








      3





      $begingroup$


      Is there any set whose every subset is equal to the set itself? It seems like this isn't possible, but maybe something similar is possible.










      share|cite|improve this question









      $endgroup$




      Is there any set whose every subset is equal to the set itself? It seems like this isn't possible, but maybe something similar is possible.







      elementary-set-theory






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      asked 2 hours ago









      lthompsonlthompson

      1269




      1269






















          2 Answers
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          $begingroup$

          In standard foundations (by which I mean ZF, or ZFC) the empty set works:
          If $Ssubset emptyset$, then $S = emptyset$.



          If you wish to do so otherwise, you’d violate the Axiom of Extensionality.






          share|cite|improve this answer









          $endgroup$





















            5












            $begingroup$

            The empty set has only itself as a subset. This is the only example because every set has the empty set as a subset.






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              2 Answers
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              5












              $begingroup$

              In standard foundations (by which I mean ZF, or ZFC) the empty set works:
              If $Ssubset emptyset$, then $S = emptyset$.



              If you wish to do so otherwise, you’d violate the Axiom of Extensionality.






              share|cite|improve this answer









              $endgroup$


















                5












                $begingroup$

                In standard foundations (by which I mean ZF, or ZFC) the empty set works:
                If $Ssubset emptyset$, then $S = emptyset$.



                If you wish to do so otherwise, you’d violate the Axiom of Extensionality.






                share|cite|improve this answer









                $endgroup$
















                  5












                  5








                  5





                  $begingroup$

                  In standard foundations (by which I mean ZF, or ZFC) the empty set works:
                  If $Ssubset emptyset$, then $S = emptyset$.



                  If you wish to do so otherwise, you’d violate the Axiom of Extensionality.






                  share|cite|improve this answer









                  $endgroup$



                  In standard foundations (by which I mean ZF, or ZFC) the empty set works:
                  If $Ssubset emptyset$, then $S = emptyset$.



                  If you wish to do so otherwise, you’d violate the Axiom of Extensionality.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 1 hour ago









                  user458276user458276

                  763212




                  763212























                      5












                      $begingroup$

                      The empty set has only itself as a subset. This is the only example because every set has the empty set as a subset.






                      share|cite|improve this answer









                      $endgroup$


















                        5












                        $begingroup$

                        The empty set has only itself as a subset. This is the only example because every set has the empty set as a subset.






                        share|cite|improve this answer









                        $endgroup$
















                          5












                          5








                          5





                          $begingroup$

                          The empty set has only itself as a subset. This is the only example because every set has the empty set as a subset.






                          share|cite|improve this answer









                          $endgroup$



                          The empty set has only itself as a subset. This is the only example because every set has the empty set as a subset.







                          share|cite|improve this answer












                          share|cite|improve this answer



                          share|cite|improve this answer










                          answered 1 hour ago









                          Ross MillikanRoss Millikan

                          298k24200373




                          298k24200373






























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