I made this problem:
$f(x)=e^{f^{\prime \prime}}$
I have just been taught the first derivative, and was thinking about what if the derivative depended upon it own derivative. I understand that $e^x$ is its "own" derivative, but the problem I made I was thinking that the first derviative is not logical, because to know the first derivative you then must know the 2nd or 3rd derviative, it seems self-referenecing.
Is the problem I made, a real problem or just some abstract idea?