If all barrels are gray steel and some barrels have open tops.
return barrels ;return #1 that are steel ;return #2 that are gray ;return number of  #1 ;return number of  #3 ;return if  #4 is equal to  #5 ;return tops of #1 ;return #1 where  #7 are open ;return number of  #8 ;return if  #9 is at least one ;return if  #9 is lower than #4 ;return if  both  #10 and #11 are true ;return if  both  #6 and #12 are true
['select', 'filter', 'filter', 'aggregate', 'aggregate', 'boolean', 'project', 'comparative', 'aggregate', 'boolean', 'boolean', 'boolean', 'boolean']