Here is a link https://arxiv.org/abs/2009.04374 https://arxiv.org/abs/2009.04374 to the paper you are probably talking about. Coming from DeepMind (and with For

Here is a link https://arxiv.org/abs/2009.04374 https://arxiv.org/abs/2009.04374 to the paper you are probably talking about. Coming from DeepMind (and with Former world champion Vladimir Kramnik as a coauthor), they studied a bunch of chess variants by training AlphaZero to play on them. In addition to no-castling, they also studied variants where pawns can always move two steps forward, and where it's possible to capture your own pieces.