2010-03-13 ago removed old CVS Ids;
2008-02-11 ago added Id;
2008-02-11 ago Made theory names in ZF disjoint from HOL theory names to allow loading both developments
2005-06-17 ago migrated theory headers to new format
2001-12-19 ago separation of the AC part of Main into Main_ZFC, plus a few new lemmas