Task: Question Decomposition
Input (English): question: what is the lowest cost fare that delta has between boston and san francisco 
Output (English): #1 return flights 
#2 return #1 on  delta 
#3 return #2 between boston 
#4 return #3 and  san francisco 
#5 return fares of #4 
#6 return #4 where #5 is  lowest