[rjpcjamc] pawn on last rank

pawn allowed on 8th rank:

• N.  (orthodox chess: promotion forced)
• Y.
  1. pawn is allowed to move to 8th rank and remain a pawn:
     • N.  (the only way a pawn can be on 8th rank is that it must have started there, so this can only happen in compositions.  this is a chess variant in only the slightest sense.)
     • Y.
  2. pawn on 8th (could have started there, or moved there) is allowed to promote in a later turn:
     • N.  (moving a pawn to the 8th rank but voluntarily keeping it a completely useless pawn is therefore the ultimate underpromotion.  challenge: compose, probably stalemate.)
     • Y.  (delayed promotion)

5 possibilities.  note that 1 and 2 are orthogonal (Cartesian product).  2 of the possibilities (Y1N2N and Y1N2Y) are relevant only for compositions.  Y1Y2N is the composition challenge.