Definition:Cauchy Product

Definition
Let $A := \displaystyle \sum_{n \mathop = 0}^\infty a_n$ and $B := \displaystyle \sum_{n \mathop = 0}^\infty b_n$ be two series.

The Cauchy product $C$ of $A$ and $B$ is defined as:
 * $\displaystyle C := \sum_{n \mathop = 0}^\infty c_n = \sum_{n \mathop = 0}^\infty a_n \cdot \sum_{n \mathop = 0}^\infty b_n$

where:
 * $\displaystyle \forall n \in \N: c_n = \sum_{k \mathop = 0}^n a_k b_{n-k} = \sum_{k \mathop = 0}^n a_{n-k} b_k$