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Given a total recursive function, can you always compute its fixed-point?


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We know from Kleene's recursion theorem that if $f$ is total recursive, there must be an integer $n$ for which $varphi_n=varphi_{f(n)}$. My question is: for every $f$ total recursive, is there a computable (total) procedure that computes such a point?



ie: $exists g.forall f.varphi_{g(n)}=varphi_{f(g(n))}$.










share|cite|improve this question











$endgroup$

















    2












    $begingroup$


    We know from Kleene's recursion theorem that if $f$ is total recursive, there must be an integer $n$ for which $varphi_n=varphi_{f(n)}$. My question is: for every $f$ total recursive, is there a computable (total) procedure that computes such a point?



    ie: $exists g.forall f.varphi_{g(n)}=varphi_{f(g(n))}$.










    share|cite|improve this question











    $endgroup$















      2












      2








      2





      $begingroup$


      We know from Kleene's recursion theorem that if $f$ is total recursive, there must be an integer $n$ for which $varphi_n=varphi_{f(n)}$. My question is: for every $f$ total recursive, is there a computable (total) procedure that computes such a point?



      ie: $exists g.forall f.varphi_{g(n)}=varphi_{f(g(n))}$.










      share|cite|improve this question











      $endgroup$




      We know from Kleene's recursion theorem that if $f$ is total recursive, there must be an integer $n$ for which $varphi_n=varphi_{f(n)}$. My question is: for every $f$ total recursive, is there a computable (total) procedure that computes such a point?



      ie: $exists g.forall f.varphi_{g(n)}=varphi_{f(g(n))}$.







      computability






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      share|cite|improve this question













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      edited 1 hour ago







      NetHacker

















      asked 1 hour ago









      NetHackerNetHacker

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          $begingroup$

          The proof of the recursion theorem is constructive: it gives you an algorithm to compute $n$ from $f$. See for example these notes of Rebecca Weber.






          share|cite|improve this answer









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            $begingroup$

            The proof of the recursion theorem is constructive: it gives you an algorithm to compute $n$ from $f$. See for example these notes of Rebecca Weber.






            share|cite|improve this answer









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              2












              $begingroup$

              The proof of the recursion theorem is constructive: it gives you an algorithm to compute $n$ from $f$. See for example these notes of Rebecca Weber.






              share|cite|improve this answer









              $endgroup$
















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                2








                2





                $begingroup$

                The proof of the recursion theorem is constructive: it gives you an algorithm to compute $n$ from $f$. See for example these notes of Rebecca Weber.






                share|cite|improve this answer









                $endgroup$



                The proof of the recursion theorem is constructive: it gives you an algorithm to compute $n$ from $f$. See for example these notes of Rebecca Weber.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 26 mins ago









                Yuval FilmusYuval Filmus

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