How to invoke a library function from another library function (defined in another element)?

Let's say I have Element1 including function f1:

def f1() {
  return 1
}

I tried to invoke f1 from f2 defined in Element2. Both elements are in __LIBRARY__ logic.

def f2() {
  return lib.Element1.f1() + 1
}

and I got an error "No such property: lib".

I also tried:

def f2() {
  return Element1.f1() + 1
}

which works in a regular logic but in the library I'm getting error "No such property: Element1".

I'm calling f2 in this way:

lib.Element2.f2()

Element1 is defined before Element2.

What is wrong? Is there any way to call f1 from f2?