public static Proposition stringtoProposition(String s){
		
		switch(s){
		
		case "Facing East":			return Proposition.IS_FACING_EAST;
		case "Facing West":		return Proposition.IS_FACING_WEST;
		case "Facing North":		return Proposition.IS_FACING_NORTH;
		case "Facing South":	return Proposition.IS_FACING_SOUTH;
		case "Next to a Beeper":		return Proposition.NEXT_TO_BEEPER;		
		case "Front is Clear":			return Proposition.IS_FRONT_CLEAR;
		case "Right is Clear":			return Proposition.IS_RIGHT_CLEAR;
		case "Left is Clear":			return Proposition.IS_LEFT_CLEAR;
	
		}
		
		return null;
	}