Tree.java

import java.util.Iterator;


public interface Tree extends Iterable{
		Position root();
		Position parent(Position p) throws IllegalArgumentException;
		Iterable<Position> children(Position p) throws IllegalArgumentException;

		int numChildren(Position p) throws IllegalArgumentException;
		boolean isInternal(Position p) throws IllegalArgumentException;
		boolean isExternal(Position p) throws IllegalArgumentException;
		boolean isRoot(Position p) throws IllegalArgumentException;
		int size();
		boolean isEmpty();

		Iterator iterator();
		Iterable<Position> positions();
		public Position replace(Position p, String e)throws IllegalArgumentException;
}