  On a convex polygonal chessboard, the number of combinatorial types of
nonattacking configuration of three identical chess riders with $r$ moves, such
as queens, bishops, or nightriders, equals $r(r^2+3r-1)/3$, as conjectured by
Chaiken, Hanusa, and Zaslavsky (2019). Similarly, for any number of identical
3-move riders the number of combinatorial types is independent of the actual
moves.
