>Why not create a .H file full of EXTERNAL declarations?

I created a file FournierTransformationFunction.h. In that file, I tried with this syntax:

#DEFINE IsCookie

That didn't work. So, I tried with this:

#DEFINE IsCookie()

That didn't work. So, I tried with this:

FUNCTION IsCookie
RETURN .F.

How should I enter those functions in the header file in order to them to be recognized at compile time?