public VertexSet getNeighbourhood(City city){
		
		 if (cityList.containsID(city.getID())) {
	            
	            VertexSet result = new VertexSet();
	            City cityOne;
	            City cityTwo;
	            for (Path p : pathList) {
	                cityOne = p.getFirstCity();
	                cityTwo = p.getSecondCity();
	                if (cityOne.equals(city)) {
	                    if (!result.containsID(cityTwo.getID())) {
	                        result.addVertex(cityTwo);
	                    }
	                    
	                } else if (cityTwo.equals(city)) {
	                    if (!result.containsID(cityOne.getID())) {
	                        result.addVertex(cityOne);
	                    }
	                }
	            }
	            
	            return result;
	        }else{
	            return null;
	        }        
	}