# Definition:Power of Element/Magma

## Definition

Let $\struct {S, \circ}$ be a magma which has no identity element.

Let $a \in S$.

Let the mapping $\circ^n a: \N_{>0} \to S$ be recursively defined as:

$\forall n \in \N_{>0}: \circ^n a = \begin{cases} a & : n = 1 \\ \paren {\circ^r a} \circ a & : n = r + 1 \end{cases}$

The mapping $\circ^n a$ is known as the $n$th power of $a$ (under $\circ$).

### Notation

Let $\circ^n a$ be the $n$th power of $a$ under $\circ$.

The usual notation for $\circ^n a$ in a general algebraic structure is $a^n$, where the operation is implicit and its symbol omitted.

In an algebraic structure in which $\circ$ is addition, or derived from addition, this can be written $n a$ or $n \cdot a$, that is, $n$ times $a$.

Thus:

$a^1 = \circ^1 a = a$

and in general:

$\forall n \in \N_{>0}: a^{n + 1} = \circ^{n + 1} a = \paren {\circ^n a} \circ a = \paren {a^n} \circ a$

## Also defined as

Some treatments do not define the power of an element for a magma whose operation is non-associative.