18. A Rook cannot perpetually chase an unprotected Cannon even if the Cannon is perpetually threatening to checkmate, has a check, or has a check and a chase. A Rook also cannot perpetually chase an unprotected Cannon even if both Cannon's reacting moves are attacking two different pieces. (See example in in Diagram 32 to 38)

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Diagram 32: Red (in Capital) moves first

R89 c15
R95 c51
R59 c15
R95 c51
R59 ...

.

.

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Diagram 33: Red (in Capital) moves first

R21 c98
R12 c89
R21 c98
R12 ...

Explanation:

In Diagrams 32 and 33, Red violates the rule by having the Rook perpetually chasing the unprotected Cannon.

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Diagram 34: Red (in Capital) moves first

R32 c83
R27 c38
R72 c83
R27 c38
R72 ...
.

.

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Diagram 35: Red (in Capital) moves first

R63 c73
R37 c37
R73 c73
R37 c37
R73 ...

Explanation:

In Diagrams 34 and 35, Black's perpetually threatening to checkmate does not violate the rule but Red's perpetual chase does. Red has to change or lose.

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Diagram 36: Red (in Capital) moves first

R27 c37
R73 c73
R37 c37
R73 c73
R37 ...

Explanation:

Black Cannon's attack on the two Red Knights does not violate the rule but Red Rook's perpetually chasing the Black Cannon does. Red has to change.

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Diagram 37: Red (in Capital) moves first

R8+1 c1+1
R8-1 c1-1
R8+1 c1+1
R8-1 c1-1
R8+1 ....

Explanation:

Black Cannon's "one check and one chase" is allowed but not Red Rook's perpetual chasing of the Black Cannon. Red has to change.

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Diagram 38: Red (in Capital) moves first

R17 c38
R72 c83
R27 c38
R72 c83
R27 ...

Explanation:

Black Cannon's one check and one chase do not violate the rule, Red Rook's perpetual chasing of the Black Cannon does. Red has to change.

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