About @Eq and double integral

[Dominique Crétel]

Hi all,

How to get a beautiful double integral symbol ?

Here is what I've done :
@Eq { big int big int sub Sigma f(x) dx }
but the result is not so pretty !

I'd like something like here : 
http://personal.maths.surrey.ac.uk/st/S.Gourley/double_int.pdf

Thanks

Dominique Cretel