Mappings from keys to indices. 
  Simple maps represent 1:1 mappings from keys to items. The Keys
  must be unique
  Multimaps represent 1 to many mappings from keys to items. 

*) -has $RO_MAP $MAP -has MAP_INCL MAP -has H_MAP -has $RO_MULTIMAP $MULTIMAP    -- Multi-maps -has RO_MULTIMAP_INCL MULTIMAP_INCL MULTIMAP -has H_MULTIMAP		   -- Hash multi-map -has B_TREE BT_NODE BT_NELEM
       -- Implemenation of (a,b) trees, which are a kind of $MAP    -has TEST_BTREE BT_NODE_DBG B_TREE_DBG -has TEST_MAP -has TEST_MULTIMAP