I assume most people on PSE know a bit of chess
With white to move, this is checkmate (1. Qb7#):
That's boring. Let's try something more interesting. With black to move, black can FORCE white to checkmate (1... Qxb7+ 2. Qxb7#):
We can go another step. In this position, white can force black to force white to checkmate (1. Qxb7+ Qxb7+ 2. Qxb7#):
I'm going to call this a forced checkmate in 2 (an abuse of traditional problems where you have to force checkmate in 2).
I can do forced checkmate in 12 (1... Qxb7+ 2. Qxb7+ Qxb7+ 3. Qxb7+ Qxb7+ 4. Qxb7+ Qxb7+ 5. Qxb7+ Qxb7+ 6. Qxb7+ Qxb7+ 7. Qxb7#):
Can you do better?
- There must be exactly one line after the first move, otherwise it is not strictly forced and I have to think too much.
- The position must be theoretically possible (so not 10 queens of one colour, 11 bishops of one colour, etc.)