The following is a recursive definition of $a^{n}:$ $$\begin{aligned}a^{1} &=a \\a^{n+1} &=a^{n} \cdot a
\end{aligned}$$ Prove, by induction, that$$a^{n+m}=a^{n} \cdot a^{m}$$ $$\left(a^{n}\right)^{m}=a^{n m}$$.
(Don't try to be fancy: use either induction on $n$ or induction on $m,$ not both at once.)