1995-01-27 ago instance: now automatically includes defs of current thy node as witnesses;
1994-10-12 ago prove_subclass, prove_arity now exported;
1994-08-19 ago cleaned sig;
1994-07-27 ago added experimental add_defns (actually should be moved somewhere else);
1994-07-14 ago added functor signature constraint;
1994-07-06 ago various minor changes (names and comments);
1994-06-16 ago (beta release)
1994-05-26 ago axiomatic type class 'package' for Pure (alpha version);