X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=exercises%2Fassignment4.mdwn;fp=exercises%2Fassignment4.mdwn;h=6f992b37201e8e46cfdb06988b037d0ba958c7ac;hp=59baf136d5ca9494f97c9a808e310c9e0d122d66;hb=04a3866462ce63d3239b3794dbe662e0377f0616;hpb=e786697f406f29139f4116d13687b37e42594f81

diff --git a/exercises/assignment4.mdwn b/exercises/assignment4.mdwn
index 59baf136..6f992b37 100644
--- a/exercises/assignment4.mdwn
+++ b/exercises/assignment4.mdwn
@@ -103,7 +103,7 @@ For instance, `fact 0 ~~> 1`, `fact 1 ~~> 1`, `fact 2 ~~> 2`, `fact 3 ~~>
 
     Some limitations of this scheme: there is no easy way to label an inner, branching node (for example with a syntactic category like VP), and there is no way to represent a tree in which a mother node has a single daughter.
 
-    When processing a tree, you can test for whether the tree is a leaf node (that is, contains only a single number), by testing whether the length of the list is 1. This will be your base case for your recursive definitions that work on these trees.
+    When processing a tree, you can test for whether the tree is a leaf node (that is, contains only a single number), by testing whether the length of the list is 1. This will be your base case for your recursive definitions that work on these trees. (You'll probably want to write a function `leaf?` that compartmentalizes this check.)
 
     Your assignment is to write a Lambda Calculus function that expects a tree, encoded in the way just described, as an argument, and returns the sum of its leaves as a result. So for all of the trees listed above, it should return `1 + 2 + 3`, namely `6`. You can use any Lambda Calculus implementation of lists you like.