Find the id of songs that are available in mp4 format and have resolution lower than 1000.
return songs ;return formats of  #1 ;return #1 where #2 is  mp4 ;return resolutions of  #1 ;return #1 where #4 is  lower than 1000 ;return #1 of  both #3 and  #5 ;return ids of  #6
['select', 'project', 'comparative', 'project', 'comparative', 'intersection', 'project']