What's the minimal number of pieces in a legal mutual stalemate?

6.  Here are three mutual stalemate positions.  Black is lower case
in the diagrams.

W Kh8 e6 f7 h7  B Kf8 e7

        --+--+--+--+--+
          |  | k|  | K|
        --+--+--+--+--+
          | p| P|  | P|
        --+--+--+--+--+
          | P|  |  |  |
        --+--+--+--+--+
          |  |  |  |  |

W Kb1  B Ka3 b2 b3 b4 a4

        |  |  |  
        +--+--+--
        | p| p|  
        +--+--+--
        | k| p|  
        +--+--+--
        |  | p|  
        +--+--+--
        |  | K|
        +--+--+--
  
W Kf1  B Kh1 Bg1 f2 f3 h2

          |  |  |  |
        --+--+--+--+
          | p|  |  |
        --+--+--+--+
          | p|  | p|
        --+--+--+--+
          | K| b| k|
        --+--+--+--+
  

[ Restored from the V3 release of the archive. ]

Put the following configuration in one corner:

|
|  x
|  P   x
|B P   P
|K R B
+---------

("x" is a Black pawn), and the same with colors reversed in the h8
corner.

--Noam D. Elkies (elkies@zariski.harvard.edu)
  Dept. of Mathematics, Harvard University