2012-03-15 ago replacing ":" by "\<in>"
2012-03-06 ago mathematical symbols instead of ASCII
2010-03-13 ago removed old CVS Ids;
2008-02-11 ago Made theory names in ZF disjoint from HOL theory names to allow loading both developments
2007-10-07 ago modernized specifications;
2005-06-17 ago migrated theory headers to new format
2003-08-28 ago Extended the notion of letter and digit, such that now one may use greek,
2002-07-09 ago better document preparation
2002-07-02 ago Tidying and introduction of various new theorems
2002-05-15 ago better simplification of trivial existential equalities
2002-05-10 ago converted the AC branch to Isar
1998-12-28 ago new inductive, datatype and primrec packages, etc.
1997-01-03 ago Implicit simpsets and clasets for FOL and ZF
1996-02-06 ago expanded tabs
1994-07-26 ago Axiom of choice, cardinality results, etc.