Update

chess.md

@@ -29,7 +29,7 @@ Chess as a game is not and cannot be [copyrighted](copyright.md), but **can ches
 
 Fun fact 2: in 2022 a chess playing robot took and broke a finger of a 7 year old opponent lol.
 
-**How to play chess with yourself?** If you have no computer or humans to play against, you may try playing against yourself, however playing a single game against yourself doesn't really work, you know what the opponent is trying to do -- not that it's not interesting, but it's more of a search for general strategies in specific situations rather than actually playing a game. One way around this could be to play many games at once (you can use multiple boards but also just noting the positions on paper as you probably won't be able to set up 100 boards); every day you can make one move in some selected games -- randomize the order and games you play e.g. with dice rolls. The number of games along with the randomized order should make it difficult for you to remember what the opponent (you) was thinking on his turn. Of course you can record the games by noting the moves, but you may want to cover the moves (in which case you'll have to be keeping the whole positions noted) until the game is finished, so that you can't cheat by looking at the game history while playing. If this method doesn't work for you because you can keep up with all the games, at least you know got real good at chess :) { This is an idea I just got, I'm leaving it here as a note, haven't tried it yet. ~drummyfish }
+**How to play chess with yourself?** If you have no computer or humans to play against, you may try playing against yourself, however playing a single game against yourself doesn't really work, you know what the opponent is trying to do -- not that it's not interesting, but it's more of a search for general strategies in specific situations rather than actually playing a game. One way around this could be to play many games at once (you can use multiple boards but also just noting the positions on paper as you probably won't be able to set up 100 boards); every day you can make one move in some selected games -- randomize the order and games you play e.g. with dice rolls. The number of games along with the randomized order should make it difficult for you to remember what the opponent (you) was thinking on his turn. Of course you can record the games by noting the moves, but you may want to cover the moves (in which case you'll have to be keeping the whole positions noted) until the game is finished, so that you can't cheat by looking at the game history while playing. If this method doesn't work for you because you can keep up with all the games, at least you know you got real good at chess :) { This is an idea I haven't tried yet, I'm leaving it here as a note, will probably try it one day. ~drummyfish } Also check out single player chess variants.
 
 **Is there any luck or [randomness](randomness.md) in chess?** Not in the rules of game itself of course, there is no dice rolling and there is no hidden information, however luck and randomness is present in the meta game (playing as white vs black may be decided randomly, your opponent may be assigned to you randomly etc.) and then [de facto](de_facto.md) in the fact that although no information is hidden, no one can ever have a complete information due to the sheer complexity of the game, so in practice playing chess involves risk, intuition and educated guessing at any human and superhuman (computer) level. So chess players do commonly talk about luck, outcome of a game is always a matter of probability which is however given by the relative skill of both players. Probability of a hobbyist beating professional in a fair game, unlike e.g. in some card games, can effectively be considered [zero](zero.md).
 
@@ -398,12 +398,12 @@ Anyway, you can try to derive your own stats, there are huge free game databases
 
 ### Variants
 
-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:
+Besides very similar games such as [shogi](shogi.md) there are many variants of chess with slight modifications of the 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 960** aka **Fischer's random** (nowadays also "freestyle chess"): 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.
@@ -416,10 +416,16 @@ Besides similar games such as [shogi](shogi.md) there are many variants of chess
 - **minichess**: Smaller chessboard, e.g. 4x4, 4x8 etc. Los Alamos chess is played at 6x6 board without bishops (also no promotion to bishop, no pawn double step, no en passant, no castling). Some are already solved (e.g. 3x3).
 - **more players**: E.g. 3 man chess or 4 player chess allow more than two players to play, some use different boards.
 - **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.
 - **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 }
+- **singleplayer**: Many attempts were made at creating [solitaire](solitaire.md) versions of chess -- in our days it's now possible to play alone against a computer or possibly try to play against self (see a note on self play at the top). Here are some of the variants designed specifically for one player:
+  - **puzzles**: Player is presented with real game situations and must find a solution, usually checkmate in N moves or finding the best move, but other goals are also possible (e.g. find the worst move). Puzzles still have to be created by someone (human or computer).
+  - **solo chess**: Similar to puzzles but there are different rules. There are only same color men which can capture each other. The goal is to capture all of them but one. Each move must be a capture, each man can only capture once and if there is a king, he has to be the last man.
+  - **safe passage**: Closer to actual game of chess, kind of similar in spirit to e.g. [peg solitaire](peg_solitaire.md). Basic setup and almost all rules stay the same as in normal chess, but there is no en passant or promotion. The easier goal is to make the two kings swap places, the harder goal is to also swap the queens. No man can move to a square where he could be captured, except for pawns which may even be captured. Changing starting positions/openings can create new challenges.
+  - ...
+- **sovereign chess**: A bigger variant of chess with different rules.
+- ...
 
 ## Playing Tips