Joseph DiMuro wrote on Mon, Oct 21, 2013 12:35 AM UTC:
Note: in this problem, it can be determined that the Black king no longer has his "move-like-a-knight" privilege. Which seems to be essential to the solution; otherwise, White would be moving into check on his second move.
What piece did Black move last? Obviously not a pawn (the pawns haven't moved yet), so he must have moved his king. Moreover, he must have moved his king from e8; all other nearby squares are either occupied or are adjacent to the White King. So Black just moved his king out of check from the pawn on d7; thus, the Black king can no longer move like a knight.
Also, I think this problem is cooked; 1.Gxb7 seems to work just as well. Please correct me if I'm wrong.
-Joseph DiMuro