What are the types of the ships that have both shiips with tonnage more than 6000 and those with tonnage less than 4000?
SELECT TYPE FROM ship WHERE Tonnage  >  6000 INTERSECT SELECT TYPE FROM ship WHERE Tonnage  <  4000
Hem 6000'den fazla tonajlı Shiips ve 4000'den az tonajı olan gemilerin tipleri nelerdir?