How many years after Isabella marry Ferdinand did they obtain a papal bull sanctioning their marriage from Pope Sixtus IV?
return Isabella did marry Ferdinand ;return Isabella and  Ferdinand did obtain a papal bull sanctioning their marriage from  Pope Sixtus IV ;return year of #1 ;return year of #2 ;return difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']