X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=week4.mdwn;h=61033f5602f114fcbc33eb8ea03e6949733f3907;hp=aa0fcf74367f9a2e1ff08b11b6f6a6876b1353b7;hb=bcc92bf29fae7f7c1423a3903dfce5ac07b97147;hpb=b8b608cf4676719fe8102794b4ffd48d1ea0a329 diff --git a/week4.mdwn b/week4.mdwn index aa0fcf74..61033f56 100644 --- a/week4.mdwn +++ b/week4.mdwn @@ -1,9 +1,6 @@ [[!toc]] -#These notes return to the topic of fixed point combiantors for one more return to the topic of fixed point combinators# - -#Q: How do you know that every term in the untyped lambda calculus has -a fixed point?# +#Q: How do you know that every term in the untyped lambda calculus has a fixed point?# A: That's easy: let `T` be an arbitrary term in the lambda calculus. If `T` has a fixed point, then there exists some `X` such that `X <~~> @@ -174,3 +171,5 @@ so A 4 x is to A 3 x as hyper-exponentiation is to exponentiation... * I hear that `Y` delivers the *least* fixed point. Least according to what ordering? How do you know it's least? Is leastness important? + +