# Symbol for function composition like a big sum

Coming from https://math.stackexchange.com/a/1097075/340174:

I would like to have something like

$$\mathop{\bigcirc}^n_{k=0} f_k \quad \text{ or } \quad \mathop{\bigcirc}^0_{k=n} f_k$$


but looking better - comparable in size and boldness to something like $\displaystyle\bigcap$ in $\displaystyle\bigcap_{k=0}^n A_k$ or to $\displaystyle\bigoplus$.

How to do this?


\end{document}