The Tree Of Scenario's (TOS) has three main branches. Lack of space, lack of mobility due to function and lack of time. First I'm going to investigate lack of space. The typical examples of immobility due to lack of space are the trap and mate. For the sake of simplicity, I take mate as illustration.
Work on the box
We talked a lot about the imaginary box that is used to contain the hostile king. There are a few scenario's that are based on working on the box.
- Work on the material of the box. Your own pieces are “soft”. Which means that the king can walk “through” them. While the king cannot walk “through” his own pieces. The “hard” pieces of the opponent are the perfect blockaders. Hence it is best to use the enemy pieces to build the box.
- Plugging a hole in the box. Sometimes a king can skedaddle out of the box when he feels itchy. You must keep the box closed.
- Breaking the box open. When the king is surrounded by its own pieces, you can't deliver the final check. In that case you have to pry the box open. With a sacrifice for instance.
- Squeezing the box. When the king has too much room to manoeuver, you must shrink it.
For other pieces than the king, the box can sometimes be quite big. It can comprise the control of a whole diagonal or file.
Chasing the king
When the king is not in the box yet, you must chase him into it. Since the king is very sensitive for checks, you can chase him over quite a distance.
What types of functions do we have? From the perspective of the opponent:
- covering a piece
- covering a square
- blocking an attacker
- keeping your attacker occupied with defense by attacking a piece that is defended by your attacker
- Keeping your attackers busy with fencing off a counter attack.
There are the following scenario's related to function:
- Harass the functional piece
- Exchange the functional piece for a less functional piece
- Capture the functional piece, so you can exploit the fact that it can no longer exert its function
- Win the piece since it isn't allowed to abandon its function
- Deflect the functional piece by forcing it to exert one of its duties while abandoning the other duty
Somehow I have the uneasy feeling I'm forgetting something.
Lack of time
In the case of a puzzle database like CT, a lot of problems are presented with a piece already hanging or being outnumbered. These positions are a bit unnatural, since they start in the middle of something. When you play a game, you know how the position came about. A single target has no time to escape since you have to move first. Usually there are two scenario's to complicate matters:
- Before you can take the hanging or outnumbered piece, you must first fence off a counter attack
- After you have taken the target, you have to fence off a counter attack
A duplo attack has two targets which are attacked with just one move. The two targets and the attacker(s) have a complex geometrical relationship. The targets must be either unprotected or insufficient protected. Scenario's:
- The targets can escape if one of them can make a tempo move
- The targets can escape if one can protect the other while their value is equal or less than the attacker
Especially in case of a duplo attack, there are specific preliminary moves.
- The target isn't yet standing on the target square, and is forced to walk the target square
- The attacker isn't on the attacking square, and has to make one or more tempo moves to get there
- The wrong target is on the target square, and by exchanging it, the right target is placed on the target square
- Lines must be opened first with tempo
- A combination of the above
A vast yet limited amount of scenario's is mapped out here. Of course the list is way too crude and bulky to be of any practical use yet. So that has to be the next step, summarizing this into a useful guide for the attention.