2018-05-09 wenzelm 2018-05-09 proper merge of items without term index (amending b969263fcf02);
2016-01-13 wenzelm 2016-01-13 tuned signature;
2015-08-16 wenzelm 2015-08-16 delete precisely the added rules; tuned;
2014-11-26 wenzelm 2014-11-26 renamed "pairself" to "apply2", in accordance to @{apply 2};
2014-02-25 wenzelm 2014-02-25 optimize special case according to Library.merge (see also 8fbc355100f2); no treatment for Net.merge, due to non-standard merge order;
2013-09-26 lammich 2013-09-26 Added Item_Net.retrieve_matching
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;