Update

chess.md

@@ -240,11 +240,14 @@ Threefold repetition is a rule allowing a player to claim a draw if the same pos
 
 Besides similar games such as [shogi](shogi.md) there are many variants of chess, i.e. slight modifications of rules, foremost worth mentioning is for example chess 960. The following is a list of some variants:
 
+- **3D chess**: [3D](3d.md) generalization of chess, possible are also other dimensions (4D, 5D, ... maybe even 1D?).
 - **antichess** ([suicide](suicide.md), ...): The goal is to lose all men or get stalemated, rules are a bit changed, e.g. castling and checks are removed and taking is forced.
+- **chess 324**: Chess with randomly modified starting position to prevent opening theory and draws, similar to chess 960. Here queens, knights and bishops are randomly shuffled in the start position with the condition that bishops must be on different color squares (no symmetry of position is required). Advantage against chess 960 is that otherwise the rules (i.e. basically castling) stay exactly the same, so basically any chess engine can also play chess 324 without modification.
 - **chess 960** aka **Fischer's random**: Starting position is randomly modified by shuffling the non-pawn rows (with these rules: king must be between rooks, bishops on opposite colors and black/white's positions are mirrored). The rules are the same with a slight modification to castling. This was invented by Bobby Fischer to emphasize pure chess skill as opposed to memorizing the best opening moves, he saw the opening theory as harmful to chess. Chess 960 is nowadays even advocated by some to become the "main" version of chess.
 - **[chess boxing](chess_boxing.md)**: Chess combined with box, players switch between the two games, one wins either by checkmate or knockout.
 - **crazyhouse**: When a player captures a man, it goes into his reserve. From the reserve a man can be dropped (as a man of the current player's color) to an empty square instead of making a normal move. This is a rule taken from [shogi](shogi.md).
 - **custom starting positions**: Creating custom starting positions is a big fun in itself, for example one can make an epic battle by replacing all pieces with queens, or a very strategic scenario in which both queens are trapped and have to be freed, or an asymmetric battle of many weak men versus a few stronger ones, or trollish ones such as the standard setup, only flipped vertically. Only one's imagination is the limit.
+- **different board geometries/topologies:** e.g. [non-Euclidean](non_euclidean.md) ([hyperbolic](hyperbolic.md), [spherical](spherical.md), [torus](torus.md), ...), hexagonal chess (had some considerable following) etc.
 - **different men**: Some variants use different men, e.g. empress (moves like rook and knight) or amazon (queen/knight).
 - **duck chess**: After each move players place a duck on an empty square, the duck blocks the square. The duck cannot be left on the same square, it has to be moved. There are no checks, players win by capturing the king.
 - **fog of war**: Makes chess an incomplete-information game by allowing players to only see squares they can immediately move to (this is similarly to some strategy video games).
@@ -255,8 +258,7 @@ 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.
-- **different board geometries/topologies:** e.g. [non-Euclidean](non_euclidean.md) ([hyperbolic](hyperbolic.md), [spherical](spherical.md), [torus](torus.md), ...), hexagonal chess (had some considerable following) etc.
-- **3D chess**: [3D](3d.md) generalization of chess, possible are also other dimensions (4D, 5D, ... maybe even 1D?).
+- **r-mobility** (reset mobility): Modifications of rules so that draws become impossible (on very high level chess becomes very drawish, this is one way to deal with the issue, even if it's used e.g. in tiebreaks). R-mobility basically generalizes mate/stalemate and works as follows. When the game ends (mate, stalemate, timed out, ...) the player with lowest number *Rp* (*p* is the player) wins. *Rp* is computed like this: at start and after any pawn more or capture it is set to infinity (reset). After player *p*'s move if the the number of opponent's legal moves, plus 1/2 if he's not in check, is lower than *Rp*, it becomes the new *Rp* (i.e. we take the minimum). So checkmating opponent means achieving 0 (the best possible), stalemating him achieves 1/2 etcetc.
 - **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 }
 
 ## Playing Tips
@@ -272,7 +274,7 @@ Some general tips and rules of thumb, mostly for beginners:
 - Pawn structure is very important (avoid doubled and isolated pawn, watch out for the weak back pawns etc.).
 - Watch out for back rank checkmates, make an escape square for your king.
 - Rooks want to be on open files, you also want to CONNECT them (have both guard each other). Also a rook in the opponents second row (2nd/7th rank) is pretty good.
-- Stack rooks, i.e. place them on the same open file -- this is very powerful. You can also stack two rooks and a queen and create a so call legendary triple stack which is extremely powerful.
+- Stack rooks, i.e. place them on the same open file -- this is very powerful. You can also stack two rooks and a queen and create a so called legendary triple stack which is extremely powerful.
 - If you find a good move, look for a better one. There seems to be this pattern in which if you spot a good move, it indicates that opponent's position is falling apart and usually there is a much more powerful, crashing move to play.
 - Bishops are generally seen a bit more valuable than knights, especially in pairs -- if you can trade your knight for opponent's bishop, it's often good. If your opponent has two bishops and you only have one, you want to trade yours for his so he doesn't have the pair. A knight pair is also pretty powerful though, especially when the knights are guarding each other.
 - Consider the bishop difference: one only covers white squares, the other only black ones. Take this into account when exchanging bishops, sacrificing them, placing your pieces on white vs dark squares etc.