2007-05-31 wenzelm 2007-05-31 insert: canonical argument order;
2005-11-09 wenzelm 2005-11-09 use existing exeption Empty;
2004-06-21 kleing 2004-06-21 Merged in license change from Isabelle2004
2004-03-19 paulson 2004-03-19 Removing the datatype declaration of "order" allows the standard General.order to be used. Thus we can use and instead of the slower home-grown versions.
2000-07-23 wenzelm 2000-07-23 assimilated;
2000-06-20 paulson 2000-06-20 new module for heaps