show me all the delta flights leaving or arriving at pittsburgh between 12 and 4 in the afternoon 
return flights ;return #1 on  delta ;return #2 leaving from  pittsburgh ;return #2 arriving at pittsburgh ;return #3 or  #4 ;return #5 between 12 and  4 in the afternoon
['select', 'filter', 'filter', 'filter', 'union', 'filter']