--- /dev/null
+
+#Reversing a list#
+
+How would you define an operation to reverse a list? (Don't peek at the
+[[lambda_library]]! Try to figure it out on your own.) Choose whichever
+implementation of list you like. Even then, there are various strategies you
+can use.
+
+
+
+<!--
+let list_equal =
+ \left right. left
+ ; here's our f
+ (\hd sofar.
+ ; deconstruct our sofar-pair
+ sofar (\might_be_equal right_tail.
+ ; our new sofar
+ make_pair
+ (and (and might_be_equal (not (isempty right_tail))) (eq? hd (head right_tail)))
+ (tail right_tail)
+ ))
+ ; here's our z
+ ; we pass along the fold a pair
+ ; (might_for_all_i_know_still_be_equal?, tail_of_reversed_right)
+ ; when left is empty, the lists are equal if right is empty
+ (make_pair
+ (not (isempty right))
+ (reverse right)
+ )
+ ; when fold is finished, check sofar-pair
+ (\might_be_equal right_tail. and might_be_equal (isempty right_tail))
+-->
+
+[[Implementing trees]]