Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:

Convert text to sql: What are the types of the ships that have both shiips with tonnage more than 6000 and those with tonnage less than 4000? | mission : mission_id , ship_id , code , launched_year , location , speed_knots , fate | ship : ship_id , name , type , nationality , tonnage | mission.ship_id = ship.ship_id | 

### Response:

select _ from _ where _ intersect select _ from _ where _ | select type from ship where tonnage > 6000 intersect select type from ship where tonnage < 4000