Rebuild-it puzzles

Puzzle 8: I have proof this is legal. There is only one move Black can have played that can come to this position (after you place back the bishop). Which is it (Black's last move)?

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You can always ask "what is the last move?' as an information question, not as a requirement for the solution. In that case, you as a composer, must make sure there is just one solution with just one unique last move. If you can't do that, you should drop the last move question.

That's what I will do. It only really matters to me for a few questions (7 and 8).

First post updated . Bonus questions added to puzzles 7 and 8.

I mean, I can easily make sure there is just one solution with just one unique last move, but I don't want to eraze puzzles 1 and 6, so...

Precisely! And just as you can easily make the last move unique, the solver can easily solve it. "Easy" is what you are trying to avoid in puzzles. There are retrograde puzzles where finding the last move is very hard but creating them is very hard as well and they typically do not end in check(mate) as all your puzzles. There is bad chemistry between puzzles with "last moves" and "check(mate)" because the latter makes the former very easy! Why not kill your darlings and drop the "last moves" alltogether?

Note:

Do you know that the solver must verify the last move anyway? It's part of the legality process to check there is a legal last move. You can use it in your puzzles for instance by including a "try" with good placements and checkmates but without legal last move! Which works better if it is not immediately obvious that there is no last move but it takes some (retro-)analysis to find out!

I know the solver does have to, but I don't know how rigorous people are on these forums. So it's like my way to make them a reminder.

Most of them don't which is great because you will catch them in the occasional "illegal try trap" you throw in the mix. If you don't do that then of course they can never go wrong so why ask them about it? Retrograde composers (like me) use these devices all the time under protection of the legality convention and they continue to make victims. Which we love of course!

Btw, in case this sounds theoretical, puzzle #4 is a great example. It actually demonstrates the legality trap if the solver places the queen on h4 instead of h5. If he forgets to look for legality there is 50% chance he places the queen on the wrong square. In the other 50% he is just lucky. But he will be caught out in another puzzle on some other day simply because he makes the wrong piece placements by chance. No need to force him to examine "last moves".

Multiple choice exams work the same way. You may guess some answers right but you'll fail on average if you didn't master the subject!

#9 and #10 are OK!

I was thinking that you have a lot of extra options if the placed units do not check or checkmate white straight away. White then gets a free move to defend himself but to no avail! Obviously the black forces need to be much stronger than in these puzzles and his king must be better protected!

#11 works though "forced mate" is a somewhat vague term often abused by puzzle makers on chess.com. I suppose you mean "a series of checks followed by a checkmate move". The game definition for "forced mate" is much softer. If mate follows on every response then the whole sequence counts as a "forced mate". In this puzzle though the forcing is crystal clear!

"Black has a series of checks followed by a checkmate move" is indeed what I meant for #11 by "Black has a forced mate".

Yes! Lots of illegality traps in #12 plus a good solution. If I am not mistaken, #13 has 3 solutions, 2 of which with a captureless last move, 1 with a last move capture.

That was a trap! There is no legal last move capture in standard chess for #13, en passant can't happen from a legal position (in standard chess, not chess960)!

But you are right about the second captureless one for puzzle #13... I must rework that puzzle, my bad!