import java.util.Enumeration;

/**
 * This simple interface specifies the methods for
 * data structures that implement an invertible mapping.
 */
public interface DoubleMap {
    public void insertXY(Object x, Object y);
    public Object getY(Object x);
    public Object getX(Object y);
    public boolean deleteXY(Object x, Object y);

    public Enumeration xElements();
    public Enumeration yElements();
}