Programming Tutorial Exercise 12
--------------------------------

This turns out to be a much easier way to solve the problem.  Let's
denote Stirling numbers as calls of the function `s'.

First, we store the rewrite rules corresponding to the definition of
Stirling numbers in a convenient variable:

     s e StirlingRules RET
     [ s(n,n) := 1  :: n >= 0,
       s(n,0) := 0  :: n > 0,
       s(n,m) := s(n-1,m-1) - (n-1) s(n-1,m) :: n >= m :: m >= 1 ]
     C-c C-c

Now, it's just a matter of applying the rules:

     2:  4          1:  s(4, 2)              1:  11
     1:  2              .                        .
         .

       4 RET 2       C-x (  ' s($$,$) RET     a r StirlingRules RET  C-x )

As in the case of the `fib' rules, it would be useful to put these
rules in `EvalRules' and to add a `:: remember' condition to the last
rule.