X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=exercises%2Fassignment5.mdwn;h=5dd1cbb24a6f8982e29b464a4d6a262d7b6675ae;hp=f0ee48119f8f71be65377a1df8211aa6aec92013;hb=442a8534983a824eec968ce2bb113fe60e0b1007;hpb=156112d5318daed7c47e18e982a6f8a12b498fd7

diff --git a/exercises/assignment5.mdwn b/exercises/assignment5.mdwn
index f0ee4811..5dd1cbb2 100644
--- a/exercises/assignment5.mdwn
+++ b/exercises/assignment5.mdwn
@@ -116,7 +116,7 @@ Choose one of these languages and write the following functions.
 
 6.  How would you use the function defined in problem 4 to enumerate a tree's fringe? (Don't worry about whether it comes out left-to-right or right-to-left.)
 
-7.  Write a recursive function to make a copy of a `color_tree` with the same structure and inner branch colors, but where the leftmost leaf is now labeled `0`, the second-leftmost leaf is now labeled `1`, and so on. (Here's a [[hint|assignment5 hint4]], if you need one.)
+7.  Write a recursive function to make a copy of a `color_tree` with the same structure and inner branch colors, but where the leftmost leaf is now labeled `0`, the second-leftmost leaf is now labeled `1`, and so on. (Here's a [[hint|assignment5 hint3]], if you need one.)
 
 8.  (More challenging.) Write a recursive function that makes a copy of a `color_tree` with the same structure and inner branch colors, but replaces each leaf label with the `int` that reports how many of that leaf's ancestors are labeled `Red`. For example, if we give your function a tree:
 
@@ -252,6 +252,8 @@ Again, we've left some gaps. (The use of `type` for the first line in Haskell an
 
 15. Choose one of these languages and fill in the gaps to complete the definition.
 
+<a id="occurs_free"></a>
+
 16. Write a function `occurs_free` that has the following type:
 
         occurs_free : identifier -> lambda_term -> bool
@@ -329,7 +331,7 @@ any type `α`, as long as your function is of type `α -> α` and you have a bas
         -- Or this:
         let sysf_true = (\y n -> y) :: Sysf_bool a
 
-    Note that in both OCaml and the Haskell code, the generalization `∀'a` on the free type variable `'a` is implicit. If you really want to, you can supply it explicitly in Haskell by saying:
+    Note that in both OCaml and Haskell code, the generalization `∀α` on the free type variable `α` is implicit. If you really want to, you can supply it explicitly in Haskell by saying:
 
         :set -XExplicitForAll
         let { sysf_true :: forall a. Sysf_bool a; ... }
@@ -384,7 +386,7 @@ Yet we haven't given ourselves the capacity to talk about `list [S]` and so on a
     = λf:T -> S. λxs:list. xs [T] [list [S]] (λx:T. λys:list [S]. cons [S] (f x) ys) (nil [S])
 -->
 
-*Update: Never mind, don't bother with the next three questions. They proved to be more difficult to implement in OCaml than we expected. Here is [[some explanation|assignment5 hint3]].*
+*Update: Never mind, don't bother with the next three questions. They proved to be more difficult to implement in OCaml than we expected. Here is [[some explanation|assignment5 hint4]].*
 
 19. Convert this list encoding and the `map` function to OCaml or Haskell. Again, call the type `sysf_list`, and the functions `sysf_nil`, `sysf_cons`, and `sysf_map`, to avoid collision with the names for native lists and functions in these languages. (In OCaml and Haskell you *can* say `('t) sysf_list` or `Sysf_list t`.)
 
@@ -408,7 +410,7 @@ Be sure to test your proposals with simple lists. (You'll have to `sysf_cons` up
         # k 1 true ;;
         - : int = 1
 
-    If you can't understand how one term can have several types, recall our discussion in this week's notes of "principal types". (WHERE?)
+    If you can't understand how one term can have several types, recall our discussion in this week's notes of "principal types".