legal AND illegal positions

If Black's last move was e7-e5 then 1. dxe6 e.p. followed by 2. g8=Q/R# or 1. ... O-O-O 2. b7#

If Black's last move was Ra8 or Ke8 then 1. Ke6 followed by 2. g8=Q/R#

Advice for white: capture e.p. if black denies this, then play Ke6 and claim he can't castle :p

@ pompom #34

*applause*!

Yep! The key is to realize that black could not have played e6-e5 last move, because the position before 0... e6-e5 could not occur in a legal game.

 Agreed.

Wow.

nice

CRaZinEsS!!!

Why?

Here is a position that I created from a year ago:

You can see the discussion of the puzzle here.  I posted my solution on page 2.

It's pretty simple to solve. The only pieces that can have moved are the knights and black's h pawn, and that pawn only once. The fact that black's queen is missing doesn't even matter, because knights can't give up tempi. So just count the tempi required to move the knights into those positions, add one to black, and that will tell you who it is to move.

Yes.  The trick is to see what color square the knights are on.  And black's missing queen doesn't matter, because the queen is trapped and must be captured on d8.  After the queen is captured, there's still no way the king can lose a tempo since there's only one square.

Black's h-pawn moved one square forward, but that doesn't really matter, either.  Black's rook now has three square to try to lose a tempo: g8, h8, and h7.  Usually, most pieces could lose a tempo with three squares to move to.  However, since g8 and h7 are on different ranks and files, there's no way to lose a tempo.  To lose a tempo with three squares, the rook will have to be able to move from h7 to g8, but that is not possible.

So, for positions that are legal and illegal depending on whose move it is, if the position seems to be near the start of the game, look for these things:

• no pawns are moved unless it is the a or h pawn moving one square forward
• no captures unless it is only the queen getting captured (other pieces getting captured will allow losing tempos)
• the color squares the knights are on

The nights could be captured too, of course.

Only queens can be captured.

Knights can be captured on a different color square.

Rooks can also be captured on a different color square when the knight moves.

Bishops will allow the rook or queen to lose a tempo.

Pawns also allow pieces to lose a tempo, and pawns could be captured on a different square.

That is an interesting observation.  It looks like every time a move was made the piece changed colored squares.  When a knight moves, it moves from a dark square to a light square or vise versa.  When black played h6, the pawn went from a light square to a dark square.  And the same applies to the rooks and the black king considering their limited mobility in the position.  It takes an even number of moves by white and an even number of moves by black to reach that position.  This means it can only be white's turn and never be black's turn.  It is a very nice problem.  :)

thanks :)

1st one is definately illegal.  Both kings are in check.

2nd one is legal.  White's last move was Kd3+ from c3 or d4.

Actually, if he wants to be technical, the diagram says "White to move," which would make the position impossible.

2nd position: What if the king was in h1 and it was BLACK to move?

Thanks Eebster for noticing.

Which means that the pawn came from e5, which is illegal because then it must be black to move as he is in check.

WRONG.