c.set_sum_white_elo(c0.sum_white_elo() + c1.sum_white_elo());
c.set_sum_black_elo(c0.sum_black_elo() + c1.sum_black_elo());
c.set_num_elo(c0.num_elo() + c1.num_elo());
c.set_sum_white_elo(c0.sum_white_elo() + c1.sum_white_elo());
c.set_sum_black_elo(c0.sum_black_elo() + c1.sum_black_elo());
c.set_num_elo(c0.num_elo() + c1.num_elo());