What is the missing piece (marked "?") in this configuration of a normal chess game?

BLACK

WHITE
Notice that the Black King is in check by the White Rook.

(In reply to re(6): An impossible check?? (partial spoiler) by Dej Mar)

Smullyan tks you, Dej Mar.

I ask your permission to "make a link" to your comment (answer) in the "solution posted". Doing this I won´t have to translate into english my notes about the solution (the difference is only the order of the analysis), avoiding possible mistakes.

Posted by pcbouhid on 2008-06-13 13:04:53