and { only { filter_greater { all_rows ; gross tonnage ; 4000 } } ; eq { hop { filter_greater { all_rows ; gross tonnage ; 4000 } ; type } ; general cargo ship / container ship } } = true
select the rows whose gross tonnage record is greater than 4000 . there is only one such row in the table . the type record of this unqiue row is general cargo ship  container ship .