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diff --git a/exercises/_assignment4.mdwn b/exercises/_assignment4.mdwn
index 38e3180f..f998e7ac 100644
--- a/exercises/_assignment4.mdwn
+++ b/exercises/_assignment4.mdwn
@@ -107,7 +107,7 @@ 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, 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`.)
+    (Note, though, that with *some* notions of infinite numbers, like [[!wikipedia ordinal numbers]], 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 ξ 1 <~~> ξ`, where `ξ` is the fixed
 point you found in (1).  What about `add ξ 2 <~~> ξ`?  
@@ -117,7 +117,7 @@ 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 ξ` is
 true for all (finite) natural numbers `n`.  However, the fixed point
-you found for `succ` and `(+n)` may not be a fixed point for `(*n)` or for
+you found for `succ` and `(+n)` (recall this is shorthand for `\x. add x n`) may not be a fixed point for `(*n)` or for
 `(^n)`.