added disclaimer about revised lambda->CL map

diff --git a/topics/week3_combinatory_logic.mdwn b/topics/week3_combinatory_logic.mdwn
index c15424f..0ddb446 100644 (file)
--- a/topics/week3_combinatory_logic.mdwn
+++ b/topics/week3_combinatory_logic.mdwn
@@ -175,6 +175,17 @@ used to establish a correspondence between two natural language grammars, one
 of which is based on lambda-like abstraction, the other of which is based on
 Combinatory Logic-like manipulations.
 
 of which is based on lambda-like abstraction, the other of which is based on
 Combinatory Logic-like manipulations.
 

+[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!]
+

 In order to establish the correspondence, we need to get a bit more
 official about what counts as an expression in CL.  We'll endow CL
 with an infinite stock of variable symbols, just like the lambda
 In order to establish the correspondence, we need to get a bit more
 official about what counts as an expression in CL.  We'll endow CL
 with an infinite stock of variable symbols, just like the lambda