promote into a friendly piece captured (which is back on the board). If none is
available, the promotion on last rank is impossible and the pawn cannot move.
-p Pawn promotion is possible (but not forced) on the two ranks before last.
+p.
+ Pawn promotion is possible (but not forced) on the two ranks before last,
+ only in an already captured (friendly) piece.
h3 End of the game