We have mate on both boards. My partner (right board) has g5+ and Qe6#. In my board, on Kf5, N@g3 mate or Kh4, g3#. I was definitely helped by material from the other board, but let us consider how my opponent contributed to his own demise: Black plays h5. I've seen this move before, in fact I played it as a teenager. In theory, if White eventually castles, Black can play h4 and h3 attacking the king position. If he does not castle, there is the idea of h5 and @g3, threatening gxf+. In reality, it makes it easier for White to attack. The Black h-pawn can no longer protect g6 or g5. I start my attack on the dark squares with Bg5. f6 is not advisable for Black because it leaves g6 weak: I am continuing my attack. I am not only attacking c7, but also d6. I offer a piece to continue my attack on the dark squares, c7, e7 and f8: So there was cxd, N@c7+ with the idea of getting the rook for the piece I sacrificed. He plays Kf8....