15. One or two cannons cannot perpetually chase a rook even if the rook is protected, or both of the rook's reacting moves are attacking an unprotected piece. (See examples in Diagram 18 through 25.)

Diagram 18: Red moves first

C4-1 r++2
C4-2 r+-2
C4+2 r++2
C4-2 r+-2
C4+2 ....

Explanation:
Red's cannon perpetually chases the protected Black rook. Red will be ruled a loss.

Diagram 19: Red moves first

C2-1 r4-2
C2+2 r4+2
C2-2 r4-2
C2+2 ....

Red's cannon keeps chasing the Black rook. In the two Black rook positions, one is when the rook is protected and the other is the rook attacks an unprotected Red cannon. To analyze which side violate the rules: Black is one chase and one idle that do not violate the rules but Red is perpetually chase. If Red refuses to change moves, Red will be ruled lose.

Diagram 20: Red moves first

C2+1 r4+2
C2-2 r4-2
C2+2 r4+2
C2-2 r4-2
C2+2 ....

Explanation:
Red cannon attacks Black rook in every move; in return Blank rook attackes Red knight or cannon in every move. Red cannon's perpetual chase of Black rook is not allowed; Black's chasing two pieces alternately is allowed. Red has to change moves or be ruled a loss.

Diagram 21: Red moves first

N5+6 r3+1
C2-1 c7+1
G5+6 c7+1
G6-5 c7-1
G5+6 c7+1
G6-5 ....

Explanation:
Red perpetually chases protected Black rook and has to change to different moves. Otherwise, it is a loss for Red.

Diagram 22 : Red moves first

C8-1 r6-1
C8+1 r6+1
C8-1 r6-1
C8+1 r6+1
C8-1 ....

Explanation:
The Red cannon perpetually chases Black rook. Although Red will lose a rook after capturing the Black rook, this is still consider an illegal perpetual chase. Red has to change moves or will be ruled lose.
Diagram 23: Red moves first

C5=7 r3=4
C7=6 r4=3
C6=7 m5+3
M7-9 m3-5
M9+7 r3=4
C7=6 r4=3
C6=7 ...

Explanation:
In Diagram 22 and 23 the Red cannon perpetually chases Black rook. Although Red will lose a rook after capturing the Black rook, this is still consider an illegal perpetual chase. Red has to change moves or will be ruled lose.

Diagram 24: Red moves first

C2+4 r4+3
C4+1 r4+2
C2-5 r4-5
C4+3 r4+3
C2+2 r4+2
C4-5 ....

Explanation:
Two Red cannons keep attacking the Black rook and in return the Black rook keeps attacking the Red knight and the pawn. Although it looks both sides "perpetually chase", the rules allow one piece to perpetually chase two or more pieces but not the other way around. Red will lose if it does not alter its moves.

Diagram 25: Red (in Capital) moves first

C2+4 r4+3
C4+1 r4+2
C4-2 r4-2
C2-3 r4-3
C4+5 ....

Explanation:
In this example the Black rook is protected but Red cannot perpetually attack it. Red will lose if not changing its moves.