Definition:Convergent Product/Normed Algebra

Definition
Let $\mathbb K$ be a division ring with absolute value $|\cdot|$.

Let $\left( A, \|\cdot\| \right)$ be a associative normed algebra over $\mathbb K$.

Let $(a_n)$ be a sequence in $A$.

The infinite product $\displaystyle \prod_{n \mathop = 1}^\infty a_n$ is convergent there exists $n_0\in\N$ such that:
 * 1) $a_n$ is invertible for $n \geq n_0$
 * 2) the sequence of partial products of $\displaystyle \prod_{n \mathop = n_0}^\infty a_n$ converges to some invertible $b\in A^\times$.