Finish lambda-prime-f2

Success. The -f2 is incredibly fast comparing with the normal and -f
version. It already annoys for >10e5, however. The complexity is O(n^2) so
every exponent increment centuplicates the time... This pure mathematical
approach has reached its limits, I think. I mean: the only thing I could
perhaps do further is to rearrange the power set members somehow to reduce
the number of divisions but I fear I can't.

So I dropped a somewhat better idea for a new algorithm in the TODO. The
related stuff lies already on a paper next to me. Anyway, the program is
still to be written and the presentation to be prepared for 21st...