X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=exercises%2F_assignment4.mdwn;h=38e3180f6f8d79c83e9d965496023f53041aaedb;hp=33c7e779c648643843d734ea71696bb54252c593;hb=701998a14b92fc759963d258f2e425587a246d48;hpb=5c234a526ad9ecc96ae9d17b6f74de53a0354444
diff --git a/exercises/_assignment4.mdwn b/exercises/_assignment4.mdwn
index 33c7e779..38e3180f 100644
--- a/exercises/_assignment4.mdwn
+++ b/exercises/_assignment4.mdwn
@@ -107,18 +107,18 @@ satisfies the following constraints, for any finite natural number `n`:
n ^ inf == inf
leq n inf == true
- (Note, though, that with some notions of infinite numbers, operations like `+` and `*` are defined in such a way that `inf + n` is different from `n + inf`, and does exceed `inf`.)
+ (Note, though, that with *some* notions of infinite numbers, like [[!wiki ordinal numers]], operations like `+` and `*` are defined in such a way that `inf + n` is different from `n + inf`, and does exceed `inf`.)
-9. Prove that `add 1 Î¾ <~~> Î¾`, where `Î¾` is the fixed
-point you found in (1). What about `add 2 Î¾ <~~> Î¾`?
+9. Prove that `add Î¾ 1 <~~> Î¾`, where `Î¾` is the fixed
+point you found in (1). What about `add Î¾ 2 <~~> Î¾`?
Comment: a fixed point for the successor function is an object such that it
is unchanged after adding 1 to it. It makes a certain amount of sense
to use this object to model arithmetic infinity. For instance,
depending on implementation details, it might happen that `leq n Î¾` is
true for all (finite) natural numbers `n`. However, the fixed point
-you found for `succ` may not be a fixed point for `mult n` or for
-`exp n`.
+you found for `succ` and `(+n)` may not be a fixed point for `(*n)` or for
+`(^n)`.
## Mutually-recursive functions ##