src/Pure/Isar/proof_history.ML
2006-01-14 wenzelm 2006-01-14 sane ERROR handling;
2005-08-16 wenzelm 2005-08-16 back: removed ill-defined '!' option;
2005-07-13 wenzelm 2005-07-13 export previous;
2005-06-20 wenzelm 2005-06-20 tuned;
2005-02-13 skalberg 2005-02-13 Deleted Library.option type.
2004-06-21 kleing 2004-06-21 Merged in license change from Isabelle2004
2000-05-05 wenzelm 2000-05-05 GPLed;
1999-10-05 wenzelm 1999-10-05 clear: int argument;
1999-08-26 wenzelm 1999-08-26 back: recur flag;
1999-07-06 wenzelm 1999-07-06 removed nesting (unused);
1999-05-21 wenzelm 1999-05-21 adapted to History changes;
1999-03-17 wenzelm 1999-03-17 added apply_cond_open;
1998-11-21 wenzelm 1998-11-21 added undos, redos;
1998-11-09 wenzelm 1998-11-09 Histories of proof states, with undo / redo and prev / back.