1.
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{B:24/1r1b4/B7/16/3k4}
{I:White's king has been knocked off the board. Where was it? Click the square it was on, then click Done. Hint - At some point you will probably conclude that the position is impossible and that there is no square for White's king which results in a legal position. At this moment you will be very close to finding the answer.;c3;Correct.;That's not the correct square.}]

2.
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{C}If White were to play, then his king would have to be on b3 or Black would be in check, but then White's own king would be in an impossible double check.]

3.
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Therefore Black is to play. What has White just played?]

4.
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It could not have been a bishop move, so it must have been a king move. Black could not have been in check before White's last move, so White has just moved his king from b3, possibly capturing something in the process. It follows that White's king was in double check from rook and bishop before his last move. We have almost argued ourselves into a corner because this double check appears impossible. The difference is that now there can be another black unit on the board, which is about to be captured by White's king.]

5.
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Now we are almost at the end. The only unit which could possibly make a difference is a black pawn, which could be on c3 as a result of the sequence c2-c4 b4xc3+. White then plays Kb3xc3, reaching the diagram position.]

6.
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This puzzle is based on the fact that the only way you can give a double check without moving one of the checking pieces is by means of an en passant capture.]

7.
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{B:24/1r1b4/B7/2K5/8/3k4}
Therefore White's king stands on c3.]
