import java.util.Enumeration;

public interface SimpleTree {
    int size();
    boolean isEmpty();

    Position root() throws SimpleTreeException;
    Position parent(Position position) throws SimpleTreeException;
    Enumeration children(Position position) throws SimpleTreeException;
    boolean isInternal(Position position) throws SimpleTreeException;
    boolean isExternal(Position position) throws SimpleTreeException;
    boolean isRoot(Position position) throws SimpleTreeException;
}