user13900: A friend of mine gave me this problem. It goes like this.
In a normal game of chess, the white player checks the black's king with a rook and a bishop as in the following image.
8/8/8/8/8/7k/8/3K1B1R b - - 0 1

Now the image seems a bit awkward. In the last move before the check, the white player will have moved either his rook or his bishop (but not both). Suppose that in the last move the white rook is moved, so the black king and white bishop would already be at the same position as they are now. So the black king was already checked by the bishop and hence it was impossible for the black king to remain in that position. Similarly, if the white bishop is moved in the last move, the black king would already be checked by the rook and hence it would be impossible for the king to stay in that position.
But it is assured that this position can be reached without any breach of rules. Does anyone know how this can be done?

user7657: In the first position which you've given, there could have been a white pawn on b7 and a black piece on a8 prior to that with white to move. Then by capturing the black piece with the white pawn and promoting it to a rook, the position shown would have been reached, with black to move.  The board is typically shown from the white perspective with the pawns moving up the board. 

user924: Double check is only possible by using discovered check. So either the rook check or the bishop check was discovered by moving something in between on the previous move.
I don't see how that's possible with the rook check, but it is possible with the bishop -- if the board is shown with black at the bottom, contrary to what is usually done. Then there could have been a pawn in between the black king and the white bishop, it could have captured something on h8 and promoted to a rook.
E.g.,
[FEN "3K1B1q/6P1/7k/8/8/8/8/8 w KQkq - 0 0"]

1.gxh8=R+


13900: <p>A friend of mine gave me this problem. It goes like this.</p>

<p>In a normal game of chess, the white player checks the black's king with a rook and a bishop as in the following image.</p>

<pre><code>8/8/8/8/8/7k/8/3K1B1R b - - 0 1
</code></pre>

<p>Now the image seems a bit awkward. In the last move before the check, the white player will have moved either his rook or his bishop (but not both). Suppose that in the last move the white rook is moved, so the black king and white bishop would already be at the same position as they are now. So the black king was already checked by the bishop and hence it was impossible for the black king to remain in that position. Similarly, if the white bishop is moved in the last move, the black king would already be checked by the rook and hence it would be impossible for the king to stay in that position.</p>

<p>But it is assured that this position can be reached without any breach of rules. Does anyone know how this can be done?</p>
 7657: <p>In the first position which you've given, there could have been a white pawn on b7 and a black piece on a8 prior to that with white to move. Then by capturing the black piece with the white pawn and promoting it to a rook, the position shown would have been reached, with black to move.  The board is typically shown from the white perspective with the pawns moving up the board. </p>
 924: <p>Double check is only possible by using discovered check. So either the rook check or the bishop check was discovered by moving something in between on the previous move.</p>

<p>I don't see how that's possible with the rook check, but it <em>is</em> possible with the bishop -- if the board is shown with black at the bottom, contrary to what is usually done. Then there could have been a pawn in between the black king and the white bishop, it could have captured something on h8 and promoted to a rook.</p>

<p>E.g.,</p>

<pre><code>[FEN "3K1B1q/6P1/7k/8/8/8/8/8 w KQkq - 0 0"]

1.gxh8=R+
</code></pre>
