Update

chess.md

@@ -116,6 +116,7 @@ Besides similar games such as [shogi](shogi.md) there are many variants of chess
 - **old chess**: The rules of chess itself have been changing over time (e.g. adding the 50 move rule etc.). The older rule sets can be seen as variants as well.
 - **puzzle**: For single player, chess positions are presented and the player has to find the best move or sequence of moves.
 - **racing kings**: The starting position has both players on the same side, the goal is to get one's king to the other side first.
+- **[non-Euclidean](non_euclidean.md)**: different geometries of the board, e.g. [hyperbolic](hyperbolic.md) or [spherical](spherical.md).
 - **3D chess**: [3D](3d.md) generalization of chess.
 - **randomly chosen variant**: Here a chess variant to be played is chosen at random before the game, e.g. by dice roll. { This is an idea I got, not sure if this exists or has a different name. ~drummyfish }