Manchester Guardian, 1957
1+3. The White King is invisible. Where is he?
Solution: If we try to put the wK in b3, it will be in check from bRb5 and bBd5 in an impossible way. But if we put him elsewhere, the bK will be in check from wBa4. Said check can only be explained if the wK just left square b3 and we are back to the original dilemma.
Well, not exactly the same dilemma. If the wK just left b3, he could have done so by capturing a black piece that could explain the impossible check !
Three moves ago, the position was:
Here the check is perfectly explainable. Play went on with 1. c2-c4 b4xc3ep+!! 2. Kb3xc3+. This is one more example of dirty tricks with en passant captures. In a very economical setting.
Finally, the White King must be on c3.