Seeking a particular problem I recall seeing a problem in Games magazine, probably in the early 1990s, that required the solver to deduce that a capture en passant was possible (not just because that's the only way to get a solution, but using retrograde analysis). I recall that all the pieces (including pawns) on the board were congregated in one corner &mdash; if I recall correctly they were all in the first three files and the last four ranks. The solver was required to mate in a small number of moves, possibly two. Does anyone know what problem it is?
I found a problem that perfectly fits your description! I’ve played the position back a move for the double step.
[Title &quot;Kurt Keller, Stuttgarter Nachrichten &amp; Südwest Presse (Ulm) 1993, Mate In Three&quot;]
[FEN &quot;5RbN/5ppk/5P1P/5P1K/8/8/8/8 b - - 0 1&quot;]
[startply &quot;2&quot;]
[startflipped &quot;&quot;]

1... g5 {Now White mates in three.} 2. fxg6+! fxg6+ (2... Kxh8 3. gxf7 Kh7 4. fxg8=Q#) 3. Nxg6 Bf7 4. Rh8# 

If the Games magazine flipped the position, then this is a problem with all pieces in one corner, on the first three files and last four ranks, a short number of moves, and an en passant key! Even it wasn’t flipped, your mind might have altered your memory. Since the problem itself is from the early 1990’s, it’s safe to to assume that the Games magazinre reprinted it for show.