Glenn is right, nW doesn't make sense. I propose that the n for the
compound move be implicit, like 'outwards'. So [WF] designates a piece
whose move consists of moving one square orthogonally to an empty square,
followed by moving one square diagonally outward to an empty or
enemy-occupied square. The piece that can make this move even if the
orthogonal square is occupied would be designated N. If the orthogonally
adjacent square must be occupied, then use
j[WF].