\begin{definition}[Definition:Positive Set]
Let $\struct {X, \Sigma}$ be a measurable space. 
Let $\mu$ be a signed measure on $\struct {X, \Sigma}$.
Let $A \in \Sigma$.
We say that $A$ is a '''$\mu$-positive set''' {{iff}}: 
:for each $E \in \Sigma$ with $E \subseteq A$ we have $\map \mu E \ge 0$.
\end{definition}