-[WARNING: the mapping from the lambda calculus to Combinatory Logic
-has been changed since the class in which it was presented. It now
-matches the presentation in Barendregt. The revised version is
-cleaner, and more elegant. If you spent a lot of time working to
-understand the original version, there's good news and bad news. The
-bad news is that things have changed. The good news is that the new
-version described the same mapping as before, but does it in a cleaner
-way. That is, the CL term that a given lambda term maps onto hasn't
-changed, only the details of how that CL term gets computed. Sorry if
-the changeup causes any distress!]
+(*Warning* This is a different mapping from the Lambda Calculus to Combinatory Logic than we presented in class (and was posted here earlier). It now matches the presentation in Barendregt 1984, and in Hankin Chapter 4 (esp. pp. 61, 65) and in Hindley & Seldin Chapter 2 (esp. p. 26). In some ways this translation is cleaner and more elegant, which is why we're presenting it.)