what are the restrictions on the cheapest one way fare between boston and oakland 
return flights ;return #1 from  boston ;return #2 to oakland ;return one way fares of #3 ;return price of #4 ;return #4 where #5 is the  lowest ;return the  restrictions of #6
['select', 'filter', 'filter', 'project', 'project', 'comparative', 'project']