*** MESSAGE REFERS TO PREVIOUS VERSION ***
support embedded values and static binding -- via implicit assignment
to src tokens (cf. assignable/assign/closure);
renamed ident/string/keyword to mk_ident/mk_string/mk_keyword;
added mk_name, mk_typ, mk_term, mk_fact, mk_attribute;
added type value with map_values etc.;
removed name_dummy, added general 'maybe' combinator;
added global/local_tyname/const;
added pretty_src, pretty_attribs;
added thm_sel (from attrib.ML);
Isabelle BUGS -- history of reported faults
===========================================
1. Symptom: hyp_subst_tac does nothing if the selected equality involves type
unknowns. Cause: it uses the simplifier, which ignores such equalities.
Fix: check for type unknowns in hypsubst/inspect_pair; change interface
function dest_eq to return the type of the equality. (lcp, 5/11/97)
2. Symptom: read_instantiate_sg has problems instantiating types in some
simultaneous instantiations (Message-id: <199710301432.PAA20594@sirius.Informatik.Uni-Bremen.DE> on isabelle-users)