Task: Question Generation
Input (English): #1 return Isabella did marry Ferdinand 
#2 return Isabella and  Ferdinand did obtain a papal bull sanctioning their marriage from  Pope Sixtus IV 
#3 return year of #1 
#4 return year of #2 
#5 return difference of #4 and  #3
Output (English): How many years after Isabella marry Ferdinand did they obtain a papal bull sanctioning their marriage from Pope Sixtus IV?