How many more residents lived in Ashkelon in 1961 than in 1955?
return Ashkelon ;return residents of #1 ;return #2 in   1961 ;return #2 in   1955 ;return number of  #3 ;return number of  #4 ;return difference of #5 and  #6
['select', 'project', 'filter', 'filter', 'aggregate', 'aggregate', 'arithmetic']