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.