Consider the simple example :
ff[x_] := x^2 gg[x_] := (ff[x] - ff[-x])^2
Let's assume I would like to expand g[x_] as a polynome of ff[x] and ff[-x], but I don't want mathematica to replace ff[x] by their value x^2 (even if it is defined in my code).
How can I do it ?
Said differently : I would like to
Expand[gg[x]] such that I would have a polynome in ff[x], ff[-x] where they are not evaluated.
I want to do it to check consistancy in some functions I defined in a more complicated code (if mathematica replaces me all the function by their values it will be hard for me to check this).