Notation for repeated application of function If I have the function $f(x)$ and I want to apply it $n$ times, what is the notation to use?
For example, would $f(f(x))$ be $f_2(x)$, $f^2(x)$, or anything less cumbersome than $f(f(x))$? This is important especially since I am trying to couple this with a limit toward infinity.

You may also use Lagrange's notation of derivative $\ f^{(n)}(x)\ $ instead of more commonly used notations $\ f^n(x)\ $ or $\ f_n(x)\ $.  
EDIT:
Or you can use left indices: $\ ^n f(x)\ $ or $\ _n f(x)\ $ or $\ ^{(n)} f(x)\ $ or $\ _{(n)} f(x)\ $.
