How many schools have students playing in goalie and mid-field positions?
return schools ;return students of  #1 ;return positions of  #2 ;return #2 where  #3 is goalie ;return #2 where  #3 is mid-field ;return #1 of  both #4 and #5 ;return number of  #6
['select', 'project', 'project', 'comparative', 'comparative', 'intersection', 'aggregate']