problem with @lag(x)

[ecofin]

hi for all,
1/ @lag(x) is the equivalent to x(-1), when i use this function a message appear see the picture bellow, but @lag(y,1) works well, what is the problem?
2/ the order difference of the function d(x,n) take natural number, I thought that in this version 8.1 it can take the real number 'I'm a little disappointed'.
thanks for all your efforts for this version.

[EViews Gareth]

1. @lag does require the second argument. We should update the documentation. Sorry!
2. I'm not sure I understand this point.

[ecofin]

1- ok!
2- I mean that the function d(x,n) can make regular and fractional differencing.

[EViews Gareth]

Got it.