How many years were there between the highest number of prisoners and the lowest?
return years ;return prisoners of #1 ;return number of  #2 for each #1 ;return #1 where #3 is highest ;return #1 where #3 is lowest ;return difference of #4 and  #5
['select', 'project', 'group', 'superlative', 'superlative', 'arithmetic']