If all the cows in the image are attached to, and pulling, something behind them.
return cows ;return something that is behind #1 ;return #1 that are attached to  #2 ;return #3 that are pulling #2 ;return number of  #1 ;return number of  #4 ;return if  #5 is equal to  #6
['select', 'project', 'filter', 'filter', 'aggregate', 'aggregate', 'boolean']