show me the flights from denver to baltimore or washington dc that arrive before or around noon 
return flights ;return #1 from  denver ;return #2 to baltimore ;return #2 to washington dc ;return #3 or  #4 ;return #5 that  arrive before noon ;return #5 that  arrive around noon ;return #6 or  #7
['select', 'filter', 'filter', 'filter', 'union', 'filter', 'filter', 'union']