2012-03-15 ago beautification and structured proofs
2012-03-15 ago replacing ":" by "\<in>"
2012-03-14 ago structured case and induct rules
2012-03-06 ago Using mathematical notation for <-> and cardinal arithmetic
2012-03-06 ago mathematical symbols instead of ASCII
2011-11-20 ago eliminated obsolete "standard";
2009-10-17 ago eliminated hard tabulators, guessing at each author's individual tab-width;
2008-02-11 ago Made theory names in ZF disjoint from HOL theory names to allow loading both developments