bool upgrade = false;
        for(int nl = 0; nl < this->chromosome.size(); ++nl) //for each
        {
            for(int m = 0; m < world->getNeighbor(0).size(); ++m)
            {
                int ml = chromsome_indexes[world->getNeighbor(nl)[m]];

                int nr;
                int mr;
                if(nl == chromosome.size()-1)
                {nr = 0;}
                else
                {nr = nl + 1;}

                if(ml == chromosome.size()-1)
                {mr = 0;}
                else
                {mr = ml + 1;}

                if(nl == ml || nl == mr || nr == ml || nr == mr)
                    continue;

                int nlc = chromosome[nl];
                int nrc = chromosome[nr];
                int mlc = chromosome[ml];
                int mrc = chromosome[mr];

                if(world->getDistance(nlc, nrc) + world->getDistance(mrc, mlc) >  world->getDistance(nlc, mrc) + world->getDistance(nrc, mrc))
                {

                    upgrade = true;
                    int i = nr;
                    int j = mr

                    while(i < j) //turn a part of the graph.
                    {
                        //std::cerr << "yay";
                        int tmp = chromosome[i];
                        chromosome[i] = chromosome[j];
                        chromosome[j] = tmp; //swaps index i and j in chromosome
                        chromsome_indexes[chromosome[i]] = i;
                        chromsome_indexes[chromosome[j]] = j;
                        ++i;
                        --j;
                    }
                }
            }
        }
        //createChromosomeIndexes();
        return upgrade;
    }