If at least one bookcase has open shelves, no backboard to it.
return bookcases ;return shelves of  #1 ;return #1 where #2 are  open ;return backboard ;return #3 with  #4 ;return #3 besides  #5 ;return number of #6 ;return if  #7 is  at least one
['select', 'project', 'comparative', 'select', 'filter', 'discard', 'aggregate', 'boolean']