Part 2: A method for NavigableSet Take a look at the NavigableSet interface. It adds a new method subSetto the methods already provided by Set. The subSet method requires that keys stored in the NavigableSet have a total order. Therefore, you'll see that the generic type is constrained to be a Comparable. The Comparable interface provides the compareTo method public interface NavigablesetT extends ComparableT extends Set Read the Java 8 APl on Comparable https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html to see what compareTo does. a) BSTSet implements the NavigableSet interface, so you need to provide an implementation of subSet. NavigableSet subSet (T fromKey, T toKey) that returns a new NavigableSet that contains all elements x, such that fromKey sx Read the Java 8 APl on Comparable https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html to see what compareTo does. a) BSTSet implements the NavigableSet interface, so you need to provide an implementation of subSet. NavigableSet subSet (T fromKey, T toKey) that returns a new NavigableSet that contains all elements x, such that fromKey sx