edits

diff --git a/week11.mdwn b/week11.mdwn
index 8eae2cc..d1bceb0 100644 (file)
--- a/week11.mdwn
+++ b/week11.mdwn
@@ -799,13 +799,15 @@ Aparently, this task, as simple as it is, is a form of computation,
 and the order in which the `'S'`s get evaluated can lead to divergent
 behavior.
 
-For now, we'll agree to always evaluate the leftmost `'S'`.
+For now, we'll agree to always evaluate the leftmost `'S'`, which
+guarantees termination, and a final string without any `'S'` in it.
 
 This is a task well-suited to using a zipper.  We'll define a function
-`tz`, which accomplished the task by mapping a char list zipper to a
-char list.  We'll call the two parts of the zipper `unzipped` and
-`zipped`; we start with a fully zipped list, and move elements to the
-zipped part by pulling the zipped down until the zipped part is empty.
+`tz` (for task with zippers), which accomplishes the task by mapping a
+char list zipper to a char list.  We'll call the two parts of the
+zipper `unzipped` and `zipped`; we start with a fully zipped list, and
+move elements to the zipped part by pulling the zipped down until the
+entire list has been unzipped (and so the zipped half of the zipper is empty).
 
 <pre>
 type 'a list_zipper = ('a list) * ('a list);;
@@ -826,13 +828,13 @@ Note that this implementation enforces the evaluate-leftmost rule.
 Task completed.
 
 One way to see exactly what is going on is to watch the zipper in
-action by tracing the execution of `t1`.  By using the `#trace`
+action by tracing the execution of `tz`.  By using the `#trace`
 directive in the Ocaml interpreter, the system will print out the
-arguments to `t1` each time it is (recurcively) called.  Note that the
+arguments to `tz` each time it is (recurcively) called.  Note that the
 lines with left-facing arrows (`<--`) show (recursive) calls to `tz`,
 giving the value of its argument (a zipper), and the lines with
 right-facing arrows (`-->`) show the output of each recursive call, a
-list.  
+simple list.  
 
 <pre>
 # #trace tz;;
@@ -869,7 +871,7 @@ The recipe for constructing the list goes like this:
 -----------------------------------------
 (3)  make a new list whose first element is 'b' and whose tail is the list constructed in step (2)
 (4)  make a new list whose first element is 'a' and whose tail is the list constructed in step (3)
-<pre>
+</pre>
 
 What is the type of each of these steps?  Well, it will be a function
 from the result of the previous step (a list) to a new list: it will