31. A Rook cannot perpetually chase a Pawn that has crossed the river.
It doesn't matter if the Pawn also threaten to capture a piece. The
Rook's side has to change or lose.
Diagram 74: Red (in Capital) moves first
The Red Rook's protecting Red Knight cannot justify perpetually
chasing the Black Pawn. Red is violating the rule and has to
Diagram 75: Red (in Capital) moves first
The Black Pawn's perpetually chasing the Red Cannon does not
violate the rule, the Red Rook's perpetually chasing the Black
Pawn does. Red is violating the rule and has to change.