Neither McCarthy nor Chaitin. We discussed this ages ago on math-fun, but my personal archive doesn't go back far enough (i.e., prior to 1997). At 06:31 PM 8/2/2012, Mike Stay wrote:

On Thu, Aug 2, 2012 at 4:44 PM, Henry Baker <hbaker1@pipeline.com> wrote:

...

BTW, who was the fellow at MIT in the early 1970's who used Lisp to teach computation theory? He had a very elegant proof of undecidability using a Lisp interpreter.

You probably mean Greg Chaitin. http://www.cs.auckland.ac.nz/~chaitin/lisp.html -- Mike Stay - metaweta@gmail.com http://www.cs.auckland.ac.nz/~mike http://reperiendi.wordpress.com