i would like the cheapest flight from pittsburgh to atlanta leaving april twenty fifth and returning may sixth 
return flights ;return #1 from pittsburgh ;return #2 to  atlanta ;return #3 leaving april twenty fifth ;return #4 returning may sixth ;return the  price of #5 ;return #5 where #6 is  the  lowest
['select', 'filter', 'filter', 'filter', 'filter', 'project', 'comparative']