-- taking notes while examining the structure, this is when I finally figured out how "two arguments were passed"
-- through the "f" and "x" functions
call a function(1)
f1()
that function is the result of another(2) function being called with a third(B) function
f1 = f2(B)
the second(2) function returns function(f) called with a forth(A) function
f2 = return ff(A)
function(x) is defined by a call to its bound function(F)
fx = F(x)
function(f) binds the passed function and returns function(x)
ff = fx(F)
finally, function(f) is called with function(A) (SEE ABOVE)

f1() -> f2(B) -> ff(A)(B) ->
fx(A)(B) -> A(B) -> B

ff(A) really means F = A & call fx(B)

-- nesting to try to understand it better
(1
  (2
    (λ f .
      (λ x .
        (f x)
      )
    )
    (λ a . a)
  )
  (λ b . b)
)

-- attempting a syntax that I understand better
λ x . (f x)     => fn X(x) { return f(x) }
λ f . X f-bound => fn F(f) { return X(f) }
λ a . a         => fn A(a) { return a }
λ b . b         => fn B(b) { return b }
anon creates F, calls it with A, then calls the result with B
                 (F(A))(B)

-- literally going in circles
F(A) -> X(A)
X(A) -> F(A)
?

-- trying to distinguish between defining functions and calling them
(
  def(
    def(λ F .
      def(λ X .
        call(F X)
      )
    )
    call(A)
  )
  call(B)
)

-- still not realizing that "x" and "f" functions are more dynamic than I expected
anon1 = { return F(A) }
F = (F){ return (X){ F(X) } }
X = (X){ return F(X) }
A = (A){ return A }
B = (B){ return B }
anon1(B)

F(B)
λ X . (F X)

-- THIS is when I finally got the whole thing
( ( (λ f . (λ x . (f x) ) ) (λ a . a) ) (λ b . b) )
B = fn(b) -> return b
A = fn(a) -> return a

(λ f . (λ x . (f x) ) ) A B
F = fn(f) -> return (λ x . (f x) )
F(A)B

λ x . (A x) B
X = fn(x) -> return A(x)
X(B) => A(B) => B

λ x . f x  OR  λ x . (f x)  OR  "(x) -> f(x)"  OR  f
"functions are equal if they give the same results on all inputs"