In the last part, we met with forks and now we can move on to the concept of fouls. At the end of the 19th century, there were no fouls in Japan in Renju, and the game was played on a 19 * 19 board, that is, they were ordinary tic-tac-toe on a 19 * 19 board. However, even then the accumulated experience of the game testified to the significant advantage of the first player. How can you limit this advantage and make the game more competitive? Recall that the goal of building a five comes down to building an open four, and it in turn comes down to building a three that is open on its turn, which is impossible without a fork. Prohibiting the first player to build basic structures like fours or triples or constructions-resources is absurd, because then he will not be able to win at all, but you can try to prevent the first player from building some of the types of forks. It is on this path and decided to go. At first, black (i.e., the first player) was forbidden to put a 4 * 4 plug, then, having decided that this was not enough to equalize the chances, in the second half of the 20th century, two more prohibited moves were introduced: a 3 * 3 plug, as well as a long row, while reducing the playing field to 15 * 15. It is these rules that have become classic for the sports version of Renju and apply to this day. However, in Japan there is still an association of players who did not accept these rules and play on board 19 * 19 with only 4 * 4 foul.

Foul – prohibited move exclusively for the first player. Setting a foul is equivalent to defeat. The foul point is a point, the course in which is prohibited.
In total, there are three fouls: three 4 * 4 plugs, 3 * 3 plugs and a long row, as well as all forks with multiplicity more than two (4 * 3 * 3, 4 * 4 * 3, etc.). The only one allowed for the first player is the 4 * 3 plug, with which Black can win. Let us turn to a detailed analysis of each foul separately.

Foul long row – move building long row

Long foul examples

The “X” in the figure is marked with foul items, the course in which is prohibited and is equivalent to defeat.

Foul 4 * 4 – a move that builds two fours and is part of each of them.

Examples of foul 4 * 4

Note: the fours do not have to be open, a foul 4 * 4 may be any two fours.

Separately allocate a linear foul 4 * 4. It is called linear due to the fact that two fours are on the same line and usually have several common stones

Examples of a linear foul 4 * 4, “!” Marked common stones, “X” – folded point

Another kind of foul is the most difficult to understand, and before moving on to it, it would be good to repeat the definition of a troika.

A triple is a construction of three stones of the same color, which is completed with a single permitted move to an open four.
Now, when we know that there are also forbidden moves, this definition acquires a new meaning for us. But how can it look in practice that the forbidden move affects the definition of a triple?

Let’s take a close look at the horizontal structure from below and diagonal from above. Are they threes? At first glance it seems that yes, because they can be completed to the open fours, go to the “X”. The problem with these constructions is that the item “X” in both cases is foul, in one case 4 * 4, in the other – a long row, which means it’s impossible to go there according to the rules. It turns out that there is not a single such move that completes these constructions to an open four, which means that despite the fact that they resemble triples, they should not be attributed to triples. But why do we need all this trouble with the definition of triples?

Foul 3 * 3 – a move that creates two triples and is part of each of them. In other words, only those constructions that are triples are involved in a foul 3 * 3.

Examples of foul 3 * 3

Will there be fouls 3 * 3 the following moves marked “?”:

It turns out no. Why? Because despite the fact that it seems that in both cases two triples participate – this is not the case. From above, the vertical construction is not a triple, since the only point that is being completed is the open four — X — is filled with another 3 * 3. It turns out that the stone under the sign “?” builds only one three, which means it is not a foul. There are no triples at all below, so each of them is floated on 4 * 4 and cannot turn into an open four.

Note: it is also necessary to remember that in the definition of the three and the four there is a phrase “included in each of them”. If there is already a three / four on the board at some point in time, the appearance of another three / four is not a foul, since the last move built only one three / four and is part of only one of them.

For training the definition of fouls there are corresponding tasks published earlier. They will help even more to master the understanding of this topic.

So, you got acquainted with the concept of fouls and learned to recognize them. But can the second player use them for their own benefit? Let’s talk about this in the next section.

In this thread, you learned:
What are fouls, why are they needed and why do they only affect