Piece diffPiece = new YouLosePiece();
if(piece == null || !(piece instanceof YouLosePiece)) {
throw new IllegalArgumentException();
}
for(String id : piece.getResourceIds()) {
diffPiece.modifyResourceValue(id, (-1)*(piece.getResourceValue(id)));
}
return diffPiece;
} catch (Exception e) {
System.out.println(e.toString());
return null;