Index Laws/Sum of Indices/Notation

Notation for Index Laws: Sum of Indices
Let $\left({S, \circ}\right)$ be a semigroup.

Let $a \in S$.

Let $a^n$ be defined as the power of an element of a magma:


 * $a^n = \begin{cases}

a : & n = 1 \\ a^x \circ a : & n = x + 1 \end{cases}$

... that is:
 * $a^n = \underbrace{a \circ a \circ \cdots \circ a}_{n \text{ copies of } a} = \circ^n \left({a}\right)$

Recall the index law for sum of indices:


 * $\circ^{n + m} a = \left({\circ^n a}\right) \circ \left({\circ^m a}\right)$

This result can be expressed:
 * $a^{n + m} = a^n \circ a^m$

When additive notation $\left({S, +}\right)$ is used, the following is a common convention:


 * $\left({n + m}\right) a = n a + m a$

or:


 * $\forall m, n \in \N_{>0}: \left({n + m}\right) \cdot a = n \cdot a + m \cdot a$