Omok is the Korean version of a game called Gomoku, or Connect-5, as the English call it. It is a game where players take turns putting pieces on a 15x15 board, in an attempt to line up 5 of their own pieces in a row. The player who manages to accomplish this wins the game. However, there are some additional rules to the game, which I will explain in more detail later.
When I was asking people for omok tips, all that I learnt can be summed up in 1 sentence. 'Use diagonals, for they are harder to detect.' I mean, seriously? That's it?
The extra rules include the double-3 rule. In simple terms, you are not allowed to place a piece on a square (or dot, if you prefer. It's easier to call it a square.) that simultaneously forms two open rows of three. A row of three is one whereby, if left alone, will require only one more piece to form a row of 4 pieces with open ends on both sides, which will lead to a win.
HOWEVER, there is an exception to this. When you or your opponent is forced to place a piece there or lose (i.e. when a row of 4 is formed, and you have to place it there to prevent the opponent from winning), you will be allowed to place your piece in the double-3 spot. In other words, if they allow you to do so, you generally win.
Rule #2: The overline rule
This is much rarer to come across. Basically, you have to form a row of FIVE pieces. Any more, and it doesn't show a win.
Were it necessary to invent a new name for this game, which reflected its essence the best one would be "structural checkers". This name reflects both the object of the game and the stages by which it is achieved (four, three etc.).
Let us now try to define simple structures. (i.e. the groups of stones, situated in the certain manner)
As soon as we start speaking about defining simple structures, it becomes vital to distinguish between two sides to these definitions. The first aspect involves internal structure of a group, i.e. amount and reciprocal location of stones constituting this group.
The second aspect is external. It describes the relationship of the given group of stones as an entity both to all the other stones, placed on the board (including those of your partner), and to the board edges. The external aspect is the most important and the most difficult one for precise understanding of omok. You won't be able to play even "five-in-a-row" if you don't understand it.
Any group can be classified by the amount of stones in it - "twos", "threes", "fours", "fives", "sixes" etc. However, this purely quantitative classification will be incomplete and unproductive. For example, not any group of 5 stones leads to victory, but only the group which forms an unbroken line. From now on, for the names of other groups we shall also use names, which will differ a little from purely quantitative understanding. We shall begin to describe simple structures from the end, from the object of the game.
Terms:
Five - five stones of the same color, which make an unbroken vertical horizontal or diagonal row. Using chess terminology we shall say that five is a mate in this game. Diagram 1 shows Black's moves (marked by white dots). which result in a winning Five, i.e. moves which form groups of five stones in the same row.
The introduced term of Five describes external conditions of the group of five stones. When describing external relations of Five, it is necessary to mention that points adjacent to Five from both sides should be free of stones of the same color. Otherwise we shall have not a Five, but a six, a seven, an eight, or a nine (a ten is impossible, as Mate inevitably precedes it). This leads to an overline, which is an unbroken row of six or more stones of the same color.
When your opponent forms a row of three, you should make it your priority to block them by putting your piece next to theirs! However, there are a few exceptions to this. The first is when you can force a win, and the second is when you can turn their three into a psuedo-three (more on this later).
In accordance with the rules of omok, moves that form an overline are do not win.
It is also better to understand the terms "Four" and "Five" not statically, but dynamically - in the process of building a winning combination.
Four - a row of four stones of the same color, which can be extended by one move to Five. Like in Chess, Four is sometimes called Check and is marked shortly "4". Diagram 2 gives some examples of Fours as well as all the moves which can change them to Fives.
It is necessary to distinguish between Four and any four stones in a row, which no move can ever change to a Five. For example, four white stones on b2, c2, d2 and e2 on diagram 4 do not make a Four. Nor will four black stones c3, d3, e3, f3 on diagram 2 make a Four if point B is occupied by a white stone.
By its internal composition, Four can be unbroken (4 stones in a row) or with a gap: 2-gap-2 or 3-gap-1 (here gap means a free point).
But we have already pointed the necessity to study external composition to determine if a given group can become a winning group. By its external composition all fours can be subdivided into two types:
Four - is a Four, which can be built to Five by the only possible move. Diagram 2 represents different Fours in the left side of the board.
They can become Fives only after making moves to points A, B, C, D, E respectively. One can say that all broken fours are Fours. But unbroken fours can also be Fours. It is clear that if the opponent does not close a Four with his next move (and in the only possible point at that), Five is inevitable.
Straight Four - is a Four which can be completed to Five from two opposite ends. Straight Fours are shown in the right side of diagram 2.
One can see that in each case two different winning moves (f, g, h) are possible. Only an unbroken Four, for which one can place a stone in a free point adjacent to it, can be a straight Four. It is obvious, that against a straight Four one's opponent has no defence, because after any of his answers (except when he makes his own Five), the next move of the player with a straight Four will be Five.
The next definition is the most difficult one among simple structures.
Three - is a row of three stones, which can be completed to a straight Four and after that to a Five. Three is also called half -checkmate and is marked shortly "3". Examples of Threes are shown in diagram 3 (marked by curved brackets), together with ways to transform them to straight Fours.
For a successful game, it is very important to be able to distinguish Three from the so-called "pseudo-three" (in other words, false or closed three), which can be transformed only to a closed Four, not a straight Four. Pseudo-three can be built to Five only if its owner has two moves in a row. There are examples of pseudo-threes in diagram 4. One can easily understand why each one of them is not a Three. The second horizontal line from the bottom gives examples of linear structures of the three and four stones, which can never be built to a Five.
By its internal composition three can be unbroken (three stones in a row) or broken: 2-gap-1. It is clear, that such linear structures of three stones like 1-gap-1-gap-1 or 2-gap-gap-1 are pseudo-threes. Like with fours threes can also be further subdivided into two types by their external composition:
Three - is a three, which can be completed to straight Four by the only possible move.
Straight Three - is a three, which can be completed to the straight Four from two different ends. Obviously, only an unbroken Three can be a straight Three. Straight Threes are shown in the left part of diagram 3, closed Threes - in the right side. Points, which correspond to winning moves are marked by letters. One can (and must!) take measures against a Three, by stopping it (thus changing it into a pseudo-three) or building a Four of his own. Otherwise, this half checkmate can become a full one (straight Four), against which there is no defense. Pseudo-three is not a method to carry a forced attack. Three-stone groups that are not situated on the same line also are a means of non-forced methods of attack.
When I was asking people for omok tips, all that I learnt can be summed up in 1 sentence. 'Use diagonals, for they are harder to detect.' I mean, seriously? That's it?
The extra rules include the double-3 rule. In simple terms, you are not allowed to place a piece on a square (or dot, if you prefer. It's easier to call it a square.) that simultaneously forms two open rows of three. A row of three is one whereby, if left alone, will require only one more piece to form a row of 4 pieces with open ends on both sides, which will lead to a win.
HOWEVER, there is an exception to this. When you or your opponent is forced to place a piece there or lose (i.e. when a row of 4 is formed, and you have to place it there to prevent the opponent from winning), you will be allowed to place your piece in the double-3 spot. In other words, if they allow you to do so, you generally win.
Rule #2: The overline rule
This is much rarer to come across. Basically, you have to form a row of FIVE pieces. Any more, and it doesn't show a win.
Were it necessary to invent a new name for this game, which reflected its essence the best one would be "structural checkers". This name reflects both the object of the game and the stages by which it is achieved (four, three etc.).
Let us now try to define simple structures. (i.e. the groups of stones, situated in the certain manner)
As soon as we start speaking about defining simple structures, it becomes vital to distinguish between two sides to these definitions. The first aspect involves internal structure of a group, i.e. amount and reciprocal location of stones constituting this group.
The second aspect is external. It describes the relationship of the given group of stones as an entity both to all the other stones, placed on the board (including those of your partner), and to the board edges. The external aspect is the most important and the most difficult one for precise understanding of omok. You won't be able to play even "five-in-a-row" if you don't understand it.
Any group can be classified by the amount of stones in it - "twos", "threes", "fours", "fives", "sixes" etc. However, this purely quantitative classification will be incomplete and unproductive. For example, not any group of 5 stones leads to victory, but only the group which forms an unbroken line. From now on, for the names of other groups we shall also use names, which will differ a little from purely quantitative understanding. We shall begin to describe simple structures from the end, from the object of the game.
Terms:
Five - five stones of the same color, which make an unbroken vertical horizontal or diagonal row. Using chess terminology we shall say that five is a mate in this game. Diagram 1 shows Black's moves (marked by white dots). which result in a winning Five, i.e. moves which form groups of five stones in the same row.
The introduced term of Five describes external conditions of the group of five stones. When describing external relations of Five, it is necessary to mention that points adjacent to Five from both sides should be free of stones of the same color. Otherwise we shall have not a Five, but a six, a seven, an eight, or a nine (a ten is impossible, as Mate inevitably precedes it). This leads to an overline, which is an unbroken row of six or more stones of the same color.
When your opponent forms a row of three, you should make it your priority to block them by putting your piece next to theirs! However, there are a few exceptions to this. The first is when you can force a win, and the second is when you can turn their three into a psuedo-three (more on this later).
In accordance with the rules of omok, moves that form an overline are do not win.
It is also better to understand the terms "Four" and "Five" not statically, but dynamically - in the process of building a winning combination.
Four - a row of four stones of the same color, which can be extended by one move to Five. Like in Chess, Four is sometimes called Check and is marked shortly "4". Diagram 2 gives some examples of Fours as well as all the moves which can change them to Fives.
It is necessary to distinguish between Four and any four stones in a row, which no move can ever change to a Five. For example, four white stones on b2, c2, d2 and e2 on diagram 4 do not make a Four. Nor will four black stones c3, d3, e3, f3 on diagram 2 make a Four if point B is occupied by a white stone.
By its internal composition, Four can be unbroken (4 stones in a row) or with a gap: 2-gap-2 or 3-gap-1 (here gap means a free point).
But we have already pointed the necessity to study external composition to determine if a given group can become a winning group. By its external composition all fours can be subdivided into two types:
Four - is a Four, which can be built to Five by the only possible move. Diagram 2 represents different Fours in the left side of the board.
They can become Fives only after making moves to points A, B, C, D, E respectively. One can say that all broken fours are Fours. But unbroken fours can also be Fours. It is clear that if the opponent does not close a Four with his next move (and in the only possible point at that), Five is inevitable.
Straight Four - is a Four which can be completed to Five from two opposite ends. Straight Fours are shown in the right side of diagram 2.
One can see that in each case two different winning moves (f, g, h) are possible. Only an unbroken Four, for which one can place a stone in a free point adjacent to it, can be a straight Four. It is obvious, that against a straight Four one's opponent has no defence, because after any of his answers (except when he makes his own Five), the next move of the player with a straight Four will be Five.
The next definition is the most difficult one among simple structures.
Three - is a row of three stones, which can be completed to a straight Four and after that to a Five. Three is also called half -checkmate and is marked shortly "3". Examples of Threes are shown in diagram 3 (marked by curved brackets), together with ways to transform them to straight Fours.
For a successful game, it is very important to be able to distinguish Three from the so-called "pseudo-three" (in other words, false or closed three), which can be transformed only to a closed Four, not a straight Four. Pseudo-three can be built to Five only if its owner has two moves in a row. There are examples of pseudo-threes in diagram 4. One can easily understand why each one of them is not a Three. The second horizontal line from the bottom gives examples of linear structures of the three and four stones, which can never be built to a Five.
By its internal composition three can be unbroken (three stones in a row) or broken: 2-gap-1. It is clear, that such linear structures of three stones like 1-gap-1-gap-1 or 2-gap-gap-1 are pseudo-threes. Like with fours threes can also be further subdivided into two types by their external composition:
Three - is a three, which can be completed to straight Four by the only possible move.
Straight Three - is a three, which can be completed to the straight Four from two different ends. Obviously, only an unbroken Three can be a straight Three. Straight Threes are shown in the left part of diagram 3, closed Threes - in the right side. Points, which correspond to winning moves are marked by letters. One can (and must!) take measures against a Three, by stopping it (thus changing it into a pseudo-three) or building a Four of his own. Otherwise, this half checkmate can become a full one (straight Four), against which there is no defense. Pseudo-three is not a method to carry a forced attack. Three-stone groups that are not situated on the same line also are a means of non-forced methods of attack.
Fork - is made simultaneously by one move. At least two threats to build a Five (i.e. Threes or Fours) must cross in the fork point. The amount of threats made by a fork is called Multiple of this fork.
It is essential to understand that Fork is not only a term of external, but also internal composition. Diagram 5 shows some examples of different Fork types: F, G, H are 3x3 Forks; A, D, E are 4x4 Forks; C, J are 4x3 Forks, I is a 3x3x4 fork, B is a 4x4x3 Fork. The last two Forks have multiple 3, all others have 2. The maximum number of forks possible is 8. By the rules of omok all the shown Forks with the exception of Forks B, C and J are prohibited.
It is necessary to be able to determine if a move is a Fork, and to determine the type of Fork.
Examples of moves shown in diagram 6 only seem to be Forks. Move A is not a 3x3 Fork, because one of the threats which compose it is false - a diagonal pseudo-three (However, it is still not allowed). The same is true for moves B and F. The move to E is not a 3x4 Fork because the horizontal group is not a Four (it can only become an Overline not a Five). Finally, move C is a prohibited 3x3x4 Fork. However, it is worth noting that the resulting three-stone diagonal group is just a pseudo-three - it can become a Four only after a move to X.
Time for the principles of tactics
If the recipes for offense and defense in omok could be found and formulated, it would mean that the algorithm of victory or draw for 1 side has been discovered and completely understood. Thankfully, it has not been found (that I know of). So, though precise calculation of game variations depending on the opponent's move is very important, intuition is of no less significance. Intuition manifests itself for each player and is realized in detailed understanding of a position. Its strength lies mostly in the player's experience and his irreproachable knowledge of the basic tactical methods of defense and offense.
I shall begin with the simplest attacking technique, the Victory by Connecting Fours (VCF). By making a four, you do not allow your opponent any alternative except stopping Four by a specified point. Diagram 7 shows the initial position and Black's victory there. Do not forget that each new stone changes the position, and may create new ways to continue the attack. (in this case, Four by the move of 1 has created the opportunity to make 4-3.
First of all, look for VCF in each position. Only when you are sure there are no VCF, do you use other methods of attack.
Practice examples:
Pay attention to the right order of the moves. Diagram 8.1 shows the initial position which ends in Black's victory. If Black selects another move sequence, e.g. making his first move to 3, then white makes his first move at 4, forcing black to move to 5, leading to a victory to white (after 4-1, or 4-A, or 4-B).
The right order of moves is still more significant when you try to reach victory by the series of continuing threes (VCT). Your opponent can try to counter-attack your Three not only by his Four, but also, as a result, create his own Three, which you must also stop if you do not have VCF. An example is given in diagram 9.
Carefully calculate your attack, and make sure your opponent has no counter plan.
Another method of a forced attack is what Gomoku players terms as Fukumi.
Fukumi is the move which threatens to win by VCF. The multiple of Fukumi is the number of moves you must make to build a winning fork 4x3. The Fukumi with the multiple 1 is called Single Fukumi. To learn how to use Fukumi effectively is a large step in improving your skill. Sometimes, Fukumi is the ONLY way to win. The position shown in diagram 10.2 is an example of this. Here, after move 1, Black has 2 opportunities to win by VCF: 3-A, 5-B. White is forced to end this threat, allowing Black the opportunity to make a Three at 3, and after that win by the fork 4x3 at C. It should be noted that if Black makes the first Fukumi at 3 (i.e. if 1-3), White can defend by playing 2-A. The same situation would appear after the first move 1-C.
Sometimes, Fukumi leads directly to victory (without intermediate moves, but at once, by Fours). It happens when two uncrossing threats are created simultaneously. On diagram 11, move 1 is double Fukumi (Do not confuse with Single Fukumi x 2). At the same time, Black by move 1 prevented any counter-threats by White.
Fukumi can be used not only at the end of the game. It is also an effective method of offense and defense in the middle of the game. After Fukumi, your opponent has a dilemma of choosing the most effective counter against your move for the threat. There is, as a rule, several possible moves. To select one from them (very often, there is only one that does not lose at once) during the game, is difficult, especially with only 30 seconds for analysis. Besides, to counter both threats, which are hidden in the potential fork, is often impossible.
This idea is illustrated by a fragment of the position in diagram 12. In the left part of the diagram, Black has played to 1, then to 3. In this case, White has three variations of the answer - A, B, or C, and the extra white stone 2. By move A, White can even intercept the initiative, making Three. In the right part of the diagram move 1 - a Fukumi - has been made. White is forced to select from 5 variations, and he cannot intercept the initiative by making Three. One of the pros of Fukumi in this situation is that White cannot counter both threats by any of his answers (Potential horizontal Three and vertical Four).
Do not hurry to make Threes and Fours, remember about the opportunities Fukumi gives. On the other hand, do not overdo it with Fukumi - sometimes only direct Fours and Threes will earn you victory.
It is allowed to apply Threes and Fukumi only when opponent does not have VCF.
Unlike the Four, Three or Fukumi, Yobi is a move which intensifies the position, and is not a forced method of attack.
It is allowed to use any Yobi, when opponent does not have his own victory by VCF, Threes, or Fukumi.
We will clarify the definition of Yobi through the examples below. Diagrams 13.1 and 13.2 illustrate two variants of Black attacks from the same initial position. Moreover, those attempts cost Black his strategic initiative. Diagram 13.3 shows a "calm" move - Yobi 1 - for that position. In the given position this move makes two uncrossing victories on different flanks.
On diagram 14 Yobi 1 makes a base for Black's attack, although it leaves White a lot of illusory defenses. Yobis used in diagrams 13 and 14 are called Semifukumi, because they create opportunities to win by series of Threes.
A special type of Yobi is going into isolation, when one's own stones are placed far away from the stones of the opponent, making numerical superiority in that flank.
It is allowed to use other types of Yobi only when the opponent does not have victory by Threes. Also, another recommendation for choosing place to make Yobi: it is most effective when it connects different flanks for a potential attack (Yobi on diagram 13).
The art of Yobi is the ultimate in attacking skill of an omok player. There are no ready-made recipes for learning this art and developing intuition for the correct time and place to make Yobi, except one - playing more, playing seriously, and analyzing every position.
Do not hurry to play all your Fours and Fukumies, give yourself a chance to make Yobi.
Now for defense.
If your opponent attacks, you must defend. However, passive defense will not be sufficient - you must try to get the initiative in order to build a counter-Four against opponent's attempts at attack. The simplest example of a Counter-Four has already been analysed in diagram 7. Black did well there and avoided White counter-Four by a correct sequence of moves.
An example of preparing a Counter-Four is shown in diagram 15. By moves 1 and 3, Black stops White's victory, as with move B, a Black Counter-Four 1-3-gap-A-B is created. In this way, Black not only manages to counter the initial White Fukumi, but also intercept the initiative.
However, not every attacking move of the opponent allows for active defense. Sometimes, you have to look for the ONLY defensive moves possible, and make them to the "strong" points of the opponent's attack.
In diagram 17, Black has made Three in move 1. It can be stopped by points A, B, or C. Black threatens to make his next move to A, and make Double Fukumi - there are two possible non-crossing forks 4x3 in points B and C. However, Fork C crosses one of the possible points where the initial Three can be stopped. Hence, the only White answer that does not lose immediately is move 2-C.
When defending, remember that the opponent's best move is also your best move. In other words, try to occupy strong points of his probable attack, points where potential threats are crossing. Determine the next strongest moves of your opponent.
However, an attempt to defend in the opponent's strong points as an answer to his direct threat is often useless. You must make defensive moves beforehand, when the opponent only prepares for an attack.
In diagram 18, Black is reverting to defense and can play either to A or B. Both these moves can stop the possible development of White's attack. But they are too passive. The best perspective for Black in this position is a move to C. Though this move does not stop White's diagonal Two by itself, it prevents its spreading to the left flank, where White can continue his attack. At the same time, this move strengthens Black's own position in that left flank, by giving him better attacking chances in future.
In an equal position the best moves are the moves, which are both defensive and offensive.
Another method of trench fighting in the middle of the game is to surround the opponent's stones. In the game shown in diagram 19 Black has got a positional advantage, as he has successfully surrounded White pieces. Black has kept space for the manoeuvre as well as several ways to start his attack with Threes.
When in positional defense, try either to surround the enemy pieces, divide them by your moves, or drive them to the board edge.
Almost all the methods above can be either defensive, or offensive, depending on the situation. However, there is also one purely-defensive method - making a Net. In diagram 20, White begins making a net by moves 2, 4, and 6, and it can be completed by moves A-J. It is a method of deep defense, but after it is built, it will take White only two moves to become active again. For instance, his move to J (with white pieces already in points 6, A, B, 4), creates four Twos, which can become Threes. Therefore, if Black does not want to be caught in White's Net, he must make his own manoeuvre - tearing the net apart by placing his piece on one of its knots. In the position above, the optimal black move is 7-E.
Although Net and its fragments is a very simple and effective method of defense, do not get carried away while making it. Your opponent will easily guess it, and break the net leaving you no good moves for attack.
It is my thread, and my choice to recreate it. The diagrams, I will create later. I have them all in mind.
Waiting for a chance to create diagrams. If there is any part you did not understand, ask. There is a good chance I will answer. Depending on the person.
