How many years apart was Albert of Saxe-Luneburg marriage to Catharina and the two underage sons marrage?
return the  marriage of Albert of  Saxe-Luneburg to Catharina ;return the  marriage of the two underage sons ;return year of #1 ;return year of #2 ;return the  difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']