What is the id of the files that are available in the format of mp4 and a resolution smaller than 1000?
return files ;return formats of #1 ;return #1 where #2 is  mp4 ;return resolutions of #1 ;return #1 where #4 is  lower than 1000 ;return id of both #3 and  #5
['select', 'project', 'comparative', 'project', 'comparative', 'intersection']