Definition:Iterated Binary Operation over Finite Set

Definition
Let $(G, *)$ be a commutative semigroup.

Let $S$ be a finite nonempty set.

Let $f : S \to G$ be a mapping.

Let $n\in\N$ be the cardinality of $S$.

Let $g : \N_{<n} \to S$ be a bijection, where $\N_{<n}$ is an initial segment of the natural numbers.

The iteration of $*$ of $f$ over $S$, denoted $\displaystyle\prod_{s\mathop\in S} f(s)$, is the indexed iteration of $*$ of the composition $f\circ g$ over $\N_{<n}$:


 * $\displaystyle\prod_{s\mathop\in S} f(s) = \displaystyle\prod_{i\mathop=0}^{n-1} f(g(i))$

Commutative Monoid
Let $G$ be a commutative monoid.

Let $S$ be a nonempty set.

Let $f : S \to G$ be a mapping

Also see

 * Iteration of Operation over Finite Set is Well-Defined
 * Iteration of Operation over Interval equals Indexed Summation, meaning that this definition can be seen as a generalization of indexed iteration
 * Definition:Summation over Finite Set
 * Definition:Product over Finite Set