How many more people populated the city in 2001 than in 1991?
return the  city ;return people populated #1 ;return #2 in  2001 ;return #2 in  1991 ;return number of  #3 ;return number of  #4 ;return difference of #5 and  #6
['select', 'project', 'filter', 'filter', 'aggregate', 'aggregate', 'arithmetic']