13. Class 1 and Class 2 each send out 4 players to compete in a table tennis singles match according to a predetermined order. Both sides start with their No. 1 players. The loser is eliminated, and the winner competes against the No. 2 player of the losing side, ... until all players on one side are eliminated, at which point the other side wins. The number of matches from the first match to the final determination of the winner, and the outcome of each match, is called a match process. Therefore, the number of possible match processes is $\qquad$ kinds.
【Answer】70
【Analysis】Comprehensive Counting: Permutations and Combinations
Since all are appearing in the order from No. 1 to No. 4, we can use 4 white balls to represent the players of Class 1, and 4 black balls to represent the players of Class 2. The following are a couple of scenarios for explanation: it can be seen that Player No. 1 of Class 1 wins against all players of Class 2;
it can be seen that Player No. 1 of Class 1 loses, and Player No. 2 of Class 1 wins against all players of Class 2; it can be seen that Player No. 1 of Class 1 wins against the first 3 players of Class 2, loses to Player No. 4 of Class 2, and Player No. 2 of Class 1 wins; $\square$
As above, the problem can be converted into the arrangement of 4 white balls and 4 black balls:
Since the balls have no order, the number of combinations can be calculated as $C_{8}^{4} \cdot C_{4}^{4}=\frac{8 \times 7 \times 6 \times 5}{4 \times 3 \times 2 \times 1}=70$ ways.