Tell the CAS that a function is the indefinite integral of another function?

[anyfoo]

If I type in:

int(2*f(x))

without definition for f, the result is a predictable:

∫2*f(x)dx

Let's suppose I know that f remains undefined, but I know that g(x) is the indefinite integral of f(x). The above expression could therefore be resolved to the indefinite integral:

2*g(x)

Can I somehow tell the CAS of this relationship?

It's important to note that I do not want to define f(x) to any specific function, but that I want to establish this relation between f(x) and the (equally undefined) g(x), for the general case.

[parisse]

You can't. It would not help much anyway.