Lambda Beta (theorical computer science)

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5 comments, last by grhodes_at_work 18 years, 6 months ago
I have to prove thate for all s which is an abstraction we have : lambda x.sx = s And I am completly stuck, I have try a prof by induction on t with s = lambda y.t but I can't prove the induction for the abstraction rule. I think about the fixpoint theorem but I am unable to apply it a useful way.Somebody as an idea ? It will be very helpful. Anyway, thank you to all of you who are going to try to do this prof. Best regards.
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This isn't homework, is it?
Yes it is !
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I could be completely off, as I don't know too much about lambda calculus yet, it's about 0400 hours and I've had little (read: no) experience doing proofs, but I'll give a hint a shot:
s = λy.t
λx.sx = λx.(λy.t)x = (... β-reduction ...) = (... α-conversion ...) = s
rule: (Lx.M)N = M[x:=N]
substitute M with sx: (Lx.sx)N = sN
(Lx.sx)N = sN but from this, I must use the eta rule to have :
Lx.sx = s, the problem is that I am not allowed to use the eta rule ( only Lambda Beta ).

Anyway I thank you very much for your answers and I am really sorry about this break of the rules, I will be more careful next time.
Homework post, closing thread. See Forum FAQ.
Graham Rhodes Moderator, Math & Physics forum @ gamedev.net

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