Merge branch 'debug-typechecking-issue-27-for-merge'
* debug-typechecking-issue-27-for-merge: Remove debugging code. Add patricia.cd file from Issue #21 Check constraints on monomorphic variables at the right place. Fix a pretty printing error for ground types (the negative part was not shown due to "worth_complement" being called twice). Rework the type variable infrastructure. Remove it from the type structure and have the auxiliary function cache the results as needed. Debugging annotations.