user8201: I just wondered: can K + 2 nightriders force a mate against bare K? (A nightrider can make an unlimited number of knight moves in any direction - it cannot change direction partway through its move.)

user9765: See my book Fairy chess endings on an n x n chessboard (2017), p. 345 and 414. The ending of king + two nightriders against bare king on board 8x8 is won for the stronger side and the longest win has 22 moves.
Also the ending king + knight + nightrider against king is a general win, see page 395.

user7297: The Wikipedia page on the Nightrider contains an example from T. R. Dawson, published in the British Chess Magazine in 1925, where a king, knight and nightrider force a mate against a lone king. I guess a similar procedure would work for two nightriders, but you have to be a little more careful to avoid stalemate.

8201: <p>I just wondered: can K + 2 nightriders force a mate against bare K? (A nightrider can make an unlimited number of knight moves in any direction - it cannot change direction partway through its move.)</p>
 9765: <p>See my book <a href="http://problem64.beda.cz/silo/kotesovec_endings_on_an_nxn_chessboard_2ed_2017.pdf" rel="nofollow noreferrer">Fairy chess endings on an n x n chessboard</a> (2017), p. 345 and 414. The ending of king + two nightriders against bare king on board 8x8 is won for the stronger side and the longest win has 22 moves.
Also the ending king + knight + nightrider against king is a general win, see page 395.</p>
 7297: <p>The <a href="https://en.wikipedia.org/wiki/Nightrider_(chess)#Examples" rel="noreferrer">Wikipedia page on the Nightrider</a> contains an example from T. R. Dawson, published in the British Chess Magazine in 1925, where a king, knight and nightrider force a mate against a lone king. I guess a similar procedure would work for two nightriders, but you have to be a little more careful to avoid stalemate.</p>
