Groundness analysis
-------------------

This analysis assigns to each operation the conditions under which
a ground (non-free) result is computed. The analysis results can be
"always ground result", "possibly non-ground result",
or "ground if arguments x1,..,xn are ground".

The idea and details of this analysis can be found in the
[ICLP'05 paper](http://www.informatik.uni-kiel.de/~mh/papers/ICLP05.html).