五つについて

由来

For years the founder of this site and his parents played across two households on the great turn-based sites of the early web — Othello with his father, more than anything, and five-in-a-row, Pente and Othello with his mother — on ItsYourTurn and GoldToken. Not a move a day — sometimes hours a day. Dozens of games open at once between the same three people, each of them checking back every few minutes to see if it was their turn, and it usually was. The sites metered it: a free account got so many moves a day, twenty on one, a hundred on another, and the family bought the memberships to lift the cap, because twenty moves was not going to last until lunch. His father played on Little Golem as well, the connoisseur’s site, against strangers from everywhere; the founder never joined it, but it was part of the same household of games.

What those sites understood has been half-forgotten since. A game between people who love each other does not need to be fast, but it does need to be kept: the position always there when you come back, the list of games waiting on you, the record of who beat whom, and a ladder to climb. It is also a way of being in the same room while living in two houses. A move is a small message that says I am here and I am thinking about you, and a hundred of them in a day is a conversation.

Itsutsu is a continuation of that, and a tribute to it. It keeps what mattered — the game waits for you, your games are listed with the ones waiting on you first, every finished game is filed, the other seat is a link you can hand to anyone — and adds what the phone in your pocket makes possible: a QR code for the other chair, a board that warns you when you are in trouble, a hint when you want one. There is no cap on moves. Play a hundred.

五つの石

Five in a row is older than almost anything else people still play for fun. In Japan it is 五目並べ, gomoku narabe, and the earliest records of it there are from the Heian period, a thousand years ago, played on a go board with go stones because those were the board and stones a house had. Similar games are claimed for China earlier still. The rules fit on a fingernail — five of your colour in a line wins — and that is exactly why it has lasted.

The trouble with a rule that simple is that the first player wins with correct play, and by the nineteenth century Japanese players knew it. The answer was renju, 連珠, “a string of pearls” — the name was coined in 1899 by the journalist Kuroiwa Ruikō, who took it from a Buddhist phrase — which handicaps black with rules against double-threes, double-fours and overlines. Renju became a serious competitive game in Japan through the twentieth century; the Renju International Federation was founded in 1988 and the first Renju World Championship was held in Kyoto in 1989. It is still played there today.

Renju’s capturing cousin, ninuki-renju, lets a pair of stones be taken by bracketing them, and it crossed the Pacific in an unlikely way: in 1977 Gary Gabrel, working at a restaurant in Stillwater, Oklahoma, turned it into Pente, which became one of the best-selling abstract games in America in the early 1980s. Pente is the game the founder and his mother played most, and the capture games here are drawn from the same well.

The line has kept growing. Connect6 was invented in 2003 by Professor I-Chen Wu in Taiwan, with one change that undoes the first-player advantage entirely: after black’s single opening stone, every turn places two. Tic-tac-toe is the oldest of the family — three-in-a-row boards are scratched into Roman floors, where it was terni lapilli — and Connect Four, the drop game, was published by Milton Bradley in 1974 and has been solved since 1988: the first player wins by starting in the middle column. The drop games here begin from that idea and wander off in eight directions.

定石

Renju is the one game in the family with a canon of named openings, and the names are a small poem. White’s second stone goes either directly beside black’s first — a direct opening — or on the diagonal from it, an indirect one, and black’s third stone then lands on one of thirteen squares in each case — twenty-six openings, each named for a moon or a star. Two of them, 花月 Kagetsu and 浦月 Hogetsu, are so strong for black that the modern tournament rules exist largely to blunt them: under the rule used at world championships since 2017, called Soosõrv-8 after the Estonian player who proposed it, the first player names the opening and the second may swap seats, and the fifth move is offered as a choice of several, so that neither side can steer into a known win.

The world championship has been held every two years since Kyoto in 1989, and the winners have come from Japan, Russia, Estonia, China and Taiwan in turn. In the current era China’s Qi Guan has won it more than once, with the strongest challenges coming from Russia and Estonia, and the games are published move by move by the Renju International Federation. The openings that decide those games are almost all indirect ones — Hogetsu and its neighbours — because a direct opening that is not Kagetsu gives white too easy a game. The Learn shelf here has a renju guide with the shapes that come out of them, and the renju board plays with the same three forbidden shapes.

Pente has its own championship. Parker Brothers ran a national tournament in the game’s first boom in the early 1980s, and since the turn of the century Pente.org has crowned an online world champion most years, with a ladder that has been running for two decades. Pente openings are not named, but there is one rule with a name: in tournament play black’s second stone must be at least three intersections from the centre, the tournament rule, which does for Pente what the swap does for renju. The capture games here offer it as the Pro opening in their set-up: first stone in the centre, black’s second outside the central 5×5.

四目落とし

Connect Four is the game in this family that a computer finished first. Milton Bradley published it in 1974; in October 1988 James Allen announced, on a Usenet newsgroup, that the first player wins, and two weeks later Victor Allis proved the same thing independently in his master’s thesis at the Vrije Universiteit Amsterdam, with a program built from nine rules of thumb rather than a search. The board has 4,531,985,219,092 legal positions. The result is exact: start in the middle column and the first player wins; start in the columns beside it and it is a draw; start anywhere else and the second player wins with correct play. John Tromp later computed the value of every opening position, and you can look any of them up.

None of that makes it an easy game for a person, which is where the hustlers come in. For a few years now the parks and squares of New York — Washington Square, Union Square, the Times Square pavements — have had a small trade in Connect Four played for money against passers-by, a regular of the game against anyone who fancies their chances, and the footage has travelled everywhere: the regulars win almost every game, sometimes while talking to someone else, because they have memorised the threats the way a chess player knows an opening. The children in the clips are the part people remember — a child of six or seven who has learned the pattern of “odd threats” beats an adult who has not, every time, and the game is short enough that a crowd gathers. That is the whole lesson of a solved game: it is not that the answer is known, it is that the answer can be learned. The drop games here begin from the standard board and wander off in eight directions, none of them solved.

和

The family is half Japanese, and the games came with the heritage. Five in a row, go, and Othello were played at home long before any of them were played through a screen, and the Japanese names beside the labels here are not decoration — they are what the games were called at the table. The name of the site is the number. 五つ, itsutsu, is simply “five”: the five stones in a row, and the five stones in the mark.

How the site looks follows from the equipment the games were played on for centuries: the ivory of a clamshell stone and the charcoal of slate, the honey of a kaya board, the washi of a printed record. The Japanese display type is a mincho face, the family a go book uses for its diagrams. Where a label has a Japanese name beside it, that name is the older one.

There is a design idea underneath as well, and it is a Japanese one: 間, ma, the space between things that gives them their shape. A board is mostly empty. A good position is read as much by where the stones are not as by where they are. The pages here try to leave room in the same way, and to say one thing at a time.

囲碁

Everything here is drawn on a go board — the grid, the star points, the clamshell-and-slate colours, the mincho face the Japanese names are set in — all borrowed from a game this site does not yet let you play, so it is worth saying what that game is. Go was invented in China more than two and a half thousand years ago and is the oldest board game still played with its rules essentially intact: a Chinese player of the fourth century BC and one of today would need a few minutes to agree the scoring and could then simply sit down. It is 围棋 weiqi in China, 바둑 baduk in Korea, and 囲碁 igo in Japan, the name that reached English. Its rules are shorter than the rules of five in a row. Players place a stone on any empty intersection, black first; a stone or a solid group of them is captured when the last empty point touching it is filled; you may not fill your own last liberty, and you may not repeat the whole board position — the ko rule, which stops two players taking the same stone back and forth for ever. Both players pass, and whoever has surrounded more of the board wins. That is all of it, and it is enough for two thousand years of argument: the first picture is a capture, and the second is the whole of life and death, because a group holding two separate eyes can never be filled and so can never be taken.

Its size is the famous part. A 19×19 board has 361 points, and the number of positions that can legally stand on it was settled exactly by John Tromp in 2016 after years of computation: 2.08 × 10¹⁷⁰, a number 171 digits long. There are something like 10⁸⁰ atoms in the observable universe, so the board has about ninety orders of magnitude more positions than the universe has atoms — which is not a flourish but the reason brute force never worked here when it had already finished Connect Four and was beating world champions at chess. Two of go’s inventions are direct ancestors of things on this site: komi, the points given to white for moving second — six and a half, or seven and a half under Chinese rules, the half existing only to make a draw impossible — and the handicap, which lets black begin with up to nine stones already placed so that two players nine grades apart can have a real game rather than a formality. Every rating and tier on the players page is chasing what the handicap did first. Go is also where computers were held off longest: chess fell in 1997, and go was expected to hold out another decade when DeepMind’s AlphaGo beat Lee Sedol four games to one in Seoul in March 2016. The moment people remember is move 37 of the second game, a shoulder hit on the fifth line that no professional would have played and that commentators first called a mistake; it won the game, and the word they reached for afterwards was beautiful. Lee took the fourth game with move 78 of his own — the last game a human has won against a top program in an even match, though in 2023 a researcher beat one again by playing a weakness another program had been set to go looking for, which is a different kind of win. You cannot play go here yet: territory, capture, ko and passing are a family of their own and a long piece of work rather than a row in a table, and the honest thing is to say so rather than leave you hunting for a link that is not there.

オセロ

Othello was the game the founder and his father played, more than any other, for hours at a stretch, and got properly good at — and it is a Japanese game, which surprises people. Its ancestor, Reversi, was an English parlour game of the 1880s, claimed by two rival inventors who argued about it in the letters pages. The game as the world plays it now — the fixed opening of four discs in the centre, the 8×8 board, the name from Shakespeare’s play about a Moor and a Venetian, black and white turning on each other — was set down by Goro Hasegawa in Japan and published there in 1973. Japan has produced most of the world champions since the first world championship in 1977, and the game’s one-line pitch, “a minute to learn, a lifetime to master,” is a Japanese slogan too.

Othello is the opposite of five in a row in one important way. In gomoku a stone is forever; in Othello nothing is yours until the end, and a board that is nearly all one colour on move fifty can belong to the other side on move sixty. Playing both for years teaches a kind of double vision: to see a position as a set of lines and as a set of edges and corners at the same time. It is on the board here now: Othello as the family played it, the older reversi with its free opening, an anti game where fewer discs wins, and a small board that can grow into the full one mid-game.

Othello also settles an old argument. Free gomoku was solved in 1993 and renju in 2001 — both wins for the first player, which is why renju’s handicaps exist — and the 6×6 Othello board was shown the same year to be a win for the second. The full board held out until 2023, when Hiroki Takizawa showed that perfect play from both sides is a draw: thirty-two discs each. No one will ever play it perfectly, which is the point.

番付

The turn-based sites ran on ladders. You challenged the player above you; a win swapped your places; the top of the list was the person nobody had beaten lately. It was a kind of rating without any arithmetic, and it made every game count for something beyond itself. Behind the arithmetic that came later stands Arpad Elo, a physics professor and chess master whose system the United States Chess Federation adopted in 1960 and the world federation in 1970. Nearly every rating you have ever seen on a games site is a descendant of it.

Five in a row has had its own championships for longer than most people expect. Renju’s world championship has run since 1989; a separate Gomoku World Championship has been held since 2009, and the two have been staged together since. The players at the top are mostly from Japan, China, Estonia, Russia and the Czech Republic, and the openings they use have names, the way chess openings do — several of them are offered here when you start a game.

On this site every finished game is filed in the record, and every named player has a rating and a tier on the players page that move with each result. Nobody is the top of a ladder yet. Somebody will be.

点数

The ladder here is Elo, the system Arpad Elo built for chess in 1960 and FIDE adopted in 1970. Its whole idea fits in a line: a rating is a prediction. If your rating is R and your opponent’s is R′, the score Elo expects you to make is E = 1 / (1 + 10^((R′ − R) / 400)), so that a four-hundred-point gap means ten to one. After the game your rating moves by K × (S − E), where S is what you actually scored — one for a win, a half for a draw, nothing for a loss — and K is how fast the number is allowed to move.

Here K is 40 for a player’s first twenty rated games and 20 after that, which is roughly what FIDE does for newcomers. Everyone starts at 1600. A player is unrated until four rated games are in — the number exists, but the page shows a dash, because a rating computed from three games is a coin toss with decimals — provisional until twenty, and established after. The site keeps one rating across all games, for the ladder, and one for each game you play, because a renju player and a Pente player are not the same player.

Most of the sites this one grew from keep a number per game type in the same spirit. FIDE and the US Chess Federation still use Elo itself; Lichess and Chess.com use its descendants, Glicko and Glicko-2, which add a measure of how sure the number is; Go in Europe uses an Elo variant with a kyu and dan scale on top; Little Golem, PlayOK and ItsYourTurn each keep an Elo-style rating for every game they offer. The dash you see beside a new name here is the honest version of what those sites show as a question mark.

One rule here is not in the arithmetic above, and it is worth knowing before anyone goes looking for easy games: a player more than four hundred points above their opponent gains nothing at all from winning. The loss still counts, and so does the draw. Elo on its own already makes a heavy favourite’s win worth almost nothing — at four hundred points the expected score is ten to one, so the gain rounds to a point or two — but almost nothing is still something, and a number that can be raised by beating beginners is a number that will be. Past that gap it simply does not move upward.

The elder sites answered the same questions differently, and Pente.org publishes its workings, which is a courtesy more sites should copy. By its own FAQ, an established player there moves on a K of 32 — more than half again as fast as ours — and 64 for a set of games rather than a single one. Its provisional players are not handled with a larger K at all but by averaging the value of the games played so far, which has the strange and candid consequence that a provisional player can lose rating by winning, if the win came against somebody far enough below them. And since May 2019 it has had a floor: a rating cannot fall more than two hundred points below the best that player has ever held. We have none of those three.

棋譜

A move here is a letter and a number — H8, the centre of a full board. The letter is the column, counting from the left; the number is the row, counting up from the bottom edge, so row 1 is the bottom of the board rather than the top. You will see it on every move in the record, beside the hint when you ask for one, and in the list of moves down the side of a game.

There is no column I. Go boards have left the letter out for as long as they have had letters on them, because I, l and 1 are the same shape at a glance and a misread coordinate is a misread game; the columns run A to H, then J. On a 19×19 board that takes the letters to T rather than S. Renju’s published records use the same convention, which is why a championship game from Kyoto can be replayed here move for move without translating anything.

The standard this belongs to is SGF, the Smart Game Format, written by Anders Kierulf in 1987 for his program Smart Go and revised into its current fourth form in the 1990s. It is the format go records are kept in, and not only go: SGF gives each game it supports a number, and GM[1] is Go, GM[2] Othello, GM[4] Gomoku and Renju, GM[11] Hex. Most of the families on this site had a number in a standard written before the web did. It is worth naming because the obvious alternative is not one: PGN is chess and only chess, and a gomoku record has no business pretending to be a chess game.

SGF does not write a point the way the board does, and it is better to be plain about that than to imply a compatibility that does not exist. An SGF point is two lowercase letters, column then row, counted from the top-left corner, with no letter skipped — so our H8 is hh, and our A1, at the bottom-left, is ao. One scheme is for reading and the other for storing, and the table below is the whole of the difference between them.

Every finished game is filed, a single game can be copied out of its replay as text, and the whole record can be taken away as a plain listing. A finished game of go, Othello, gomoku, renju or Hex can also be downloaded from its replay as an .sgf file and opened in any program that reads that game. The games SGF has no number for — the capture games, Connect6, the drop games, checkers and the rest — offer no file at all, because a file claiming one of those four numbers would be a different game wearing its name.

先達

These are the places this one learned from, and they are still there. ItsYourTurn has run turn-based games by email since 1998, from the first years of the web, and is where the founder’s family played for years. Its shape is the shape of this site: a list of games waiting on you, a list waiting on them, invitations, and a record. A free account is capped at a number of moves a day, which is why the family bought the membership; the paid tier lifts the cap and opens tournaments and the rarer games. Its catalogue is about forty games with variants, and it keeps a rating per game type.

GoldToken came soon after, around 2000, with a larger catalogue — over sixty games and their variants — and a community that felt like a club: tokens earned for playing, ladders, tournaments, a forum. The free account limits how many games you may have open at once; membership lifts that and adds more. It was the other half of the family’s evenings. Little Golem, started in 2002 by Richard Malaschitz in Slovakia, is the connoisseur’s site: Hex, Go, gomoku, Amazons, Twixt and dozens of other abstracts, many in several variants, monthly championships in each, an Elo-style rating for each, and no paid tier at all — it runs on donations. Some of the strongest players in the world of several of those games enter its championships, and the founder’s father played there for years.

Pente.org has kept ranked Pente alive online for two decades, with the tournament rule, several variants of its own, a ladder and a world championship, and membership optional. PlayOK — many still call it Kurnik, the name Marek Futrega gave it when he started it in Poland in 2001 — is where you go for a live game of gomoku against a stranger at two in the morning, with an Elo rating per game and rooms that never seem to empty. Membership numbers are the one thing none of these sites publish plainly; each has had tens of thousands of registered players at its peak, and each has a hard core that has been there for twenty years.

If you have a code, the door is here. If you do not, the learning shelf is open to everyone.