Yavalath

Yavalath is an abstract board game for two or three players, invented by a computer program called LUDI. It has an easy rule set that any player can pick up immediately, but which produces surprisingly tricky emergent play.

Yavalath is available from nestorgames, making it the first — and still only — computer-generated game to be commercially published, together with its sister game Pentalath.

In October 2011, Yavalath was ranked in the top #100 abstract board games ever invented on the BoardGameGeek database. This helped it win the GECCO "Humies" gold medal for human-competitive results in evolutionary computation for 2012.

Here is a Yavalath article in the November 2013 issue of Bitcoin magazine.

 Rules The board starts empty. Two players take turns adding a piece of their colour to an empty cell. Win by making a line-of-4 (or more) pieces of your colour. Lose by making a line-of-3 pieces of your colour beforehand. Draw if the board otherwise fills up.

No, players are not allowed to pass.

Tactics and Strategy

The key tactical play in Yavalath is the forcing move, as shown below. White move 1 forces Black to lose with the blocking move 2.

This example demonstrates two general principles of play:

1.  Unblocked lines of size 4 (separated by two empty cells) have good attacking potential.
2.  Unblocked lines of size 3 (or adjacent pairs of pieces) are vulnerable to attack.

The following figure shows the extension of principle 1 to a size 4 triangle formed by three unblocked lines of size 4. This is a strong formation that allows its owner to force a win, as shown on the right.

As a general rule of thumb, players should prevent the opponent from forming such unblocked size 4 triangles, and the first step to achieving this is to block lines of size 4 as they appear.

Games of Yavalath tend to be short, decisive and dominated by passages of forced play. Moves that offer the current player freedom of choice are therefore precious and having the initiative (move in hand) is more important than in most games. It is easy to create interesting Yavalath puzzles from board positions that emerge during actual play.

The following blocking pattern fills the board without either player winning or losing. However, this pattern requires more than twice as many pieces of one colour than the other, and hence will not occur in actual play except within subregions of the board.

Draws, although possible, are extremely rare. Players generally tend to make a fatal mistake (long sequences of forced moves can be difficult to predict correctly) or are forced to make a losing move as the number of available choices dwindles in the end game.

Annotated Sample Game

The following Yavalath game #162 was played on the Gamerz.net server in January, 2008, between the two highest-ranked players at the time.

 White   1 Opening suggested by the computer player.   3! Strong reply that establishes a size 4 line threat. Black     2? Black takes the proffered central cell. 5 Forcing move that blocks Black’s line threat.   7 White completes a size 4 triangle (blocked on one side). 4 Black blocks with their own line threat.   6 Forced reply.     8? An apparently good move that only delays the inevitable.

Move 8 appears at first to be quite strong; it completes a size 4 triangle (partially blocked) while forcing an apparently innocuous reply 9 from White. However, the ensuing forced sequence eventually yields the initiative to White.

Move 13 establishes a size 4 triangle for White, which although blocked on one side presents a win next move at cell x. Black must immediately address this threat.

 White 15 Forced reply.   17 White lines up the win. Black 14 Black foils the imminent win.   16 Forced reply.   18 Black is forced to make a line of three. Black loses.

Black’s defeat was certain after move 13 (no other reply 14 would avoid defeat) and almost as certain after move 8 as moves 9, 10, 11 and 12 were then forced. In fact, the decline of Black’s position can be traced back to their very first move 2 which allowed White to establish a strong opening formation with move 3. This opening play was first proposed by the computer player, which puts it to good use against unwary opponents.

Computer Player

yavalath.zip (34 KB, zipped)

The computer player uses an algorithm called UCT that plays a strong game. Interestingly, the UCT player will often make good tactical and strategic plays (such as the opening shown in the example above) despite having no knowledge of the game apart from its legal moves and winning conditions.

### Variants

Three-Player Version: The three-player version is played according to the same rules, except that players must block the next player's win if possible, and any player forming a line of 3 without also forming a line of 4 is removed from the game (but not their pieces).

The winner is either:
1) The last surviving player, or
2) The first player to form a line of 4.

The two-player version is deadly due to the prevalence of forced move sequences. The three-player version is just evil :)

Five-not-four: The end conditions can be extended to winning on a line of five and losing on a line of four. This version works surprisingly well but should be played on larger boards, e.g. six cells per side.

History

Yavalath rules by Ludi by Cameron Browne and copyright (c) Cyberite Ltd, December 2007.

Yavalath was designed by machine. The rules were created by a programme called Ludi that evolves rule sets from existing games into new combinations, then measures the resulting rule sets to determine whether they actually constitute viable games and, if so, how likely they are to be of interest to human players. The machine did not actually suggest the three-player version; this was a natural extrapolation of the two-player rules.

The name "Yavalath" was randomly created from a list of Tolkien-style word forms by a Markovian process.

Yavalath can be played on Richard's PBeM server - check out the help file for more details. Many thanks to the server regulars who helped test the game. Please challenge me (camb) to a game any time.

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