select D.DiskTitel from Disk D
where D.DiskID in
        (select M.DiskID from Musikstueck M
         where M.Titel = ’I love you’ and
                M.DiskID in
                  (select I.DiskID from Interpret I
                   where I.Instrument = ’Triangel’ and I.StueckID = M.StueckID))