import java.util.*;

public interface Application 
{
    	/**
         * Determines if a given position is legal and not a dead end.
         *
         * @param pos - the given position.
         *
         * @return true if pos is a legal position and not a dead end.
         */    	
	boolean isOK (Position pos);


    	/**
         * Indicates that a given position is possibly on a path to a goal.
         *
         * @param pos the position that has been marked as possibly being on a 
         *                path to a goal.
         */
	void markAsPossible (Position pos);


	/**
         * Indicates whether a given position is a goal position.
         *
         * @param pos the position that may or may not be a goal position.
         *
         * @return true if pos is a goal position; false otherwise.
     	 */	
    	boolean isGoal (Position pos);
	

	/**
         * Indicates that a given position is not on any path to a goal position.
         *
         * @param pos the position that has been marked as not being on any path to 
         *                a goal position.
         */
    	void markAsDeadEnd (Position pos);
	

	/**
         * Converts this Application object into a String object.
         *
         * @return the String representation of this Application object.
         */
	String toString();


	/**
         * Produces an Iterator object that starts at a given position.
         *
         * @param pos the position the Iterator object starts at.
         *
         * @return an Iterator object that accesses the positions directly
	 *               available from pos.           	 
	 */
	Iterator<Position> iterator (Position pos);

} // interface Application