renamed extern to extern_thm;
renamed cert/read_typ_raw to cert/read_typ_abbrev;
added cert/read_typ_syntax;
thms: NameSpace.table;
* May 2005: Rafal Kolanski, NICTA
Substantially improved retrieval of facts from theory/proof context.
* May 2005: Florian Haftmann, TUM
Several new antiquotation.
* February 2005: Lucas Dixon, University of Edinburgh
Substantially improved subst method.
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