2. What are indexes?References to your documents, efficiently ordered by keyMaintained in a tree structure, allowing fast lookup{x:1}{y:1}{x:0.5,y:0.5}{x:2,y:0.5}{x:5,y:2}{x:-4,y:10}{x:3,y:’f’} 3. Fast document lookup db.c.findOne( {_id:2} ), using index {_id:1}db.c.find( {x:2} ), using index {x:1}db.c.find( {x:{$in:[2,3]}} ), using index {x:1}db.c.find( {‘x.a’:1} ), using index {‘x.a’:1}Matches {