zlacker

Smart. It didn't occur to me to have the base case be an arbitrary function. Yours is much larger than mine. One comment: M=Nest; is a waste of characters. I tried that in my solution too, but it wound up costing me an extra character ;). So I think you're down to 75 characters. It might make sense to remove the factorial, and change the base case of u to f@f@f@f@a.

>>evanb+(OP)
Thanks, I forgot to remove M=Nest that was beneficial in my previous attempts where I used 3 Nests.

But remember:

Never forget that it is a waste of energy to do the same thing twice, and that if you know precisely what is to be done, you need not do it at all. --- E. E. ``Doc'' Smith (1930)

      ...the optimal solution avoids all pattern.
                                        --- Douglas Hofstadter (1983)

http://djm.cc/bignum-results.txt

So I would recommend to avoid things like f@f@f@f@a where there is clearly a pattern.