# [Haskell-beginners] abou the Godel Numbering for untyped lambda calculus

Algebras Math algebras2009 at googlemail.com
Mon Mar 30 21:55:25 EDT 2009

```Hi all,

I am reading the book "The lambda calculus: Its syntax and Semantics" in the
chapter about Godel Numbering but I am confused in some points.

We know for Church Numerals, we have Cn = \fx.f^n(x) for some n>=0,
i.e. C0= \fx.x and C
1 = \fx.fx.

>From the above definition, I could guess the purpose of this kind of
encoding is trying to encode numeral via terms.

How about the Godel Numbering? From definition we know people say #M is the
godel number of M and we also have [M] = C#M to enjoy the second fixed point
theorem : for all F there exists X s.t. F[X] = X.

What the mapping function # is standing for? How could I use it? What the #M
will be? How to make use of the Godel Numbering?

Thank you very much!

alg
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