We have already met with the basic structures and resources and can move on to the next important concept – the plug. Fork is a favorite tactical technique for beginner chess players. But if in chess it serves as a means of obtaining an advantage, then in Renju the construction of a fork is a vital necessity, without which it will be impossible to practically win (we will consider exceptions later). As in chess, in Renju, the plug is defined as a double threat. We have only two direct threats: the four and the three, respectively, there can be only three types of forks: 3 for 3, 4 for 4 and 4 for 3

Fork examples

The last move, forming a fork, is marked “X”. Why are forks so important in Renju and why it’s impossible to win without them? Recall that our ultimate goal to build a five was reduced to the construction of an open four, and an open four, as we know, emerges from the three. But the question is – how to get an open four if the opponent will close all our triples? Consider the following position:

If Black starts building threats, playing three and fours, then White will simply close them. White will answer B on three, White will close C to C, which will form a pair after A, and Black will finish the three to E, White will also close F, and after three C, three G will play H! After all the wagering turns out this position:

It turns out that all our efforts to build an open four of the three failed because we posed only one threat and the opponent safely closed it. However, in this position, Black has the opportunity to put a fork in the “X” point, a four is formed horizontally, and a three is diagonally. White will be forced to close the four, and Black will finish his three to the open four and win. Thus, in order to get an open four, we need a move that puts not one, but two threats at once, and the goal to build an open four is to build a fork before the opponent. However, we should not forget about the seniority of threats. Consider the following position:

White may think that they have won, so now it’s their turn and they are the first to build a double threat – 3 * 3 forks go to X. However, in response, Black goes to Y, building his own 4 * 3 forks! Despite the fact that whites were the first to build a fork, they forgot that the four as a threat are older than the three, as she lacks just one stone before the five, while the three lack two. Now, if White decides to build an open four, Black will finish his four to five and win, if White decides to close the four, then Black is the first to complete his three to the open four, which means they will win. When setting your own forks and moves in general, you need to be very careful and do not forget about the opponent’s resources. We will return to the question of the seniority of threats when we examine the more subtle methods of attack, but for now we have come close to the second difference in Renju from tic-tac-tokens, which will be discussed in the next section.

In this thread, you learned:
What is a plug and what types of plugs are
Why do we need forks, and why not win without a double threat
What role does threat seniority play and why it is important to monitor opponent’s resources