Solution

Europe Echecs 433, Apr. 1995

1+5. Black to move. What did White just play?

White did just move his King to e5, but from which square? Whatever square we try, the King was in a seemingly impossible double check.

As a matter of fact, one such double check is possible. If we assume
White did just play *n.* Kf5-e5, then the double check on f5
could have been given by an en-passant capture *n-1* ... f4xg3
e.p.

But then the capture was only legal if White did play *n-1.*
g2-g4. This move answered a check given by the bBh3, again seemingly
impossible. The trick is that this must have been a discover check,
given by some bNg4 that has been captured by the wK.

Last moves are:

*n-2* ... Ng4-(/x)e5 +

*n-1.* g2-g4 f4xg3 ep +

*n.* Kf5xNe5.

In retro-parlance, this cute problem is a "Last move (Type B)" problem with 3 precise last single moves. The 4th retro-move is not precise because it could have been any capture Ng4xe5.