\begin{definition}[Definition:Permanent]
Let $\mathbf A = \sqbrk a_n$ be a square matrix of order $n$.
That is, let:
:$\mathbf A = \begin {pmatrix}
a_{1 1} & a_{1 2} & \cdots & a_{1 n} \\
a_{2 1} & a_{2 2} & \cdots & a_{2 n} \\
 \vdots &  \vdots & \ddots & \vdots \\
a_{n 1} & a_{n 2} & \cdots & a_{n n}
\end {pmatrix}$
Let $\lambda: \N_{>0} \to \N_{>0}$ be a permutation on $\N_{>0}$.
Then the '''permanent''' of $\mathbf A$ is defined as:
:$\ds \sum_{\lambda} \paren {\prod_{k \mathop = 1}^n a_{k \map \lambda k} } = \sum_{\lambda} a_{1 \map \lambda 1} a_{2 \map \lambda 2} \cdots a_{n \map \lambda n}$
where:
:the summation $\ds \sum_\lambda$ goes over all the $n!$ permutations of $\set {1, 2, \ldots, n}$.
\end{definition}