A useful program
Marc van Woerkom
Marc.Vanwoerkom@REDACTED
Wed Aug 11 17:47:30 CEST 2004
Am Wed, 11 Aug 2004 16:41:37 +0200 (CEST) hat
Joe Armstrong <joe@REDACTED> geschrieben:
Here (attached) is a very useful program
The classical ones write themselves to stdout!
First I stumbled over such self producing programs, when I
had a look into a source distribution of gcc.
Only much later, when I took a course on theoretical
computer science (theory of computation, recursion theory)
I got a hint, why folks write such programs.
There is a selfproduction lemma, derived from the
recursion theorem.
It exists a number n from |N such that phi_n(x) = n,
where phi is the standard enumeration of the
computable
functions (of one argument)
phi : |N -> P^1
:-)
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