20 | | | | | | | | | |---------------------------------------| | | | | | | | | | 13 |---------------------------------------| 12 | | | | | | | | | |---------------------------------------| | | | | | | | | * | 5 |---------------------------------------| 4 | * | | | | | | | | +---------------------------------------+ 3 2 1

Diagram 97.

From the above explanation it is evident that in the case of an exchange the move remains unaltered if the captured pieces were located in the same system, and that the move changes if the captured pieces belonged to different systems.

Exceptions to the rule sometimes occur due to a piece having no mobility, as for instance in the position of Diagram 97 where Black, on the move, loses because his man on 28 is blocked.

THE THIRD POSITION

32        31        30
+---------------------------------------+
|    |    |    |    |    |    |    |    | 29
|---------------------------------------|
28 |  o |    |    |    |    |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 21
|---------------------------------------|
20 | oo |    | ** |    |    |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 13
|---------------------------------------|
12 | oo |    | ** |    |    |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 5
|---------------------------------------|
4 |    |    |    |    |    |    |    |    |
+---------------------------------------+

3 2 1

Diagram 98.—­White to Move and Win.

White being a man ahead appears to have an easy win; but owing to the difficulty of getting the man crowned he has a hard task before him.

If the Kings on 11 and 12 were removed White would not be able to win at all, as the Black King would go back and forth between 19 and 23.  It is, therefore, clear that in forcing a win from the position of the diagram the King on 12 must cooperate.

Another point to be borne in mind is that the following position would be a draw with White to move.

32        31        30
+---------------------------------------+
|    |    |    |    |    |    |    |    | 29
|---------------------------------------|
28 |    |    |    |    |    |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 21
|---------------------------------------|
20 |  o |    | oo |    | oo |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 13
|---------------------------------------|
12 |    |    | ** |    |    |    |    |    |
|---------------------------------------|
|    |    |    |    |    |    |    |    | 5
|---------------------------------------|
4 |    |    | ** |    |    |    |    |    |
+---------------------------------------+
3         2        1

Diagram 99.