//loop invariant
            	for (int j = 0; j < x - 1; j++){
    				for (int k = 0; k < column; k++){
    						assert comp.compare(people[j][k], people[j][k + 1]) <= 0;
    						assert comp.compare(people[j][k], people[j + 1][k]) <= 0;
    					}
    				}
            	//loop invariant