German grundform reduction
This is a rather incomplete implementaion of work done by Gudrun Putze-Meier. I have to confess that I never read her original paper. So all credit belongs to her, all bugs are mine. I tried to get some insight from an implementation of two students of mine. They remain anonymous because their work was the wost piece of code I ever saw. My code behaves mostly as their implementation did except it is about 75 times faster.