2008-04-16 wenzelm 2008-04-16 removed unused space_of; added defined, fold_static; renamed dest_table to dest_static; renamed extern_table to extern_static;
2008-04-15 wenzelm 2008-04-15 renamed dest to dest_table, and extern to extern table; added name space intern/extern;
2008-04-15 wenzelm 2008-04-15 disallow duplicate entries (weak version for merge); added hide;
2008-03-25 wenzelm 2008-03-25 support dynamic facts;
2008-03-20 wenzelm 2008-03-20 added pos_of_ref;
2008-03-20 wenzelm 2008-03-20 Facts.Named: include position;
2008-03-19 wenzelm 2008-03-19 renamed datatype thmref to Facts.ref, tuned interfaces;
2008-03-17 wenzelm 2008-03-17 replaced generic add by add_local/add_global; add_global: report/ignore duplicate bindings;
2008-03-15 wenzelm 2008-03-15 del: hide in name space;
2008-03-15 wenzelm 2008-03-15 Environment of named facts (admits overriding). Optional indexing by proposition.