Here's a question Ramana got me thinking about.  Going through the
tutorial, I see functions (p 83) which interpret just fine:

# let fib2 = define
`(fib2 0 = 1) /\
(fib2 1 = 1) /\
(fib2 (n + 2) = fib2(n) + fib2(n + 1))`;;        
val fib2 : thm =
  |- fib2 0 = 1 /\ fib2 1 = 1 /\ fib2 (n + 2) = fib2 n + fib2 (n + 1)

But how can I use fib2 to calculate Fibonacci numbers?  I suppose if I
was trying to prove something about Fibonacci numbers, HOL Light with
this definition would be great.  But this doesn't get me anything:

# `fib2 6`;;
val it : term = `fib2 6`

and here I got an error: 

# REAL_ARITH `fib2 6`;;
Exception: Failure "mk_neg".

Maybe what I'm really asking is how to use HOL Light as a CAS, I see
that at least one person, Cezary Kaliszyk, has done this:
http://cl-informatik.uibk.ac.at/users/cek/holcas.php
I bet a coauthor of Barendregt would do a good job here, but I'd guess
there a way in HOL Light to crank out some numbers from functions.

-- 
Best,
Bill 

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