2011-05-14 wenzelm 2011-05-14 slightly more efficient claset operations, using Item_Net to maintain rules in canonical order;
2010-04-23 wenzelm 2010-04-23 Item_Net/Named_Thms: export efficient member operation;
2009-11-16 wenzelm 2009-11-16 member/cons: slightly more correct treatment of multi-index, notably empty one;
2009-11-01 wenzelm 2009-11-01 allow multi-index; more scalable merge; renamed delete to remove, and insert to update (standard naming conventions); tuned;
2009-03-17 wenzelm 2009-03-17 turned structure NetRules into general Item_Net, which is loaded earlier;