Symbol for iterated composition

Question

For numbers $x_1, \ldots, x_n$ one may write $$ \sum_{i = 1}^n x_i $$ for what might otherwise informally be written $x_1 + \cdots + x_n$.

For functions $f_1, \ldots, f_n$ is there similar notation for what might otherwise informally be written as $f_1 \circ \cdots \circ f_n$?

Answer 1

Hint: The paper Notation for Iteration of Functions, Iteral by Valerii Salov from 2012 gives a survey of used notation of iterated functions. He also proposes a new notation, a so-called Iteral-operator to describe iteration of functions.