\begin{definition}[Definition:Probability Measure/Definition 3]
Let $\EE$ be an experiment.
Let $\Omega$ be the sample space on $\EE$.
Let $\Sigma$ be the event space of $\EE$.
A '''probability measure on $\EE$''' is a mapping $\Pr: \Sigma \to \R$ which fulfils the following axioms:
{{begin-axiom}}
{{axiom | n = \text I
        | q = \forall A \in \Sigma
        | ml= \map \Pr A
        | mo= \ge
        | mr= 0
}}
{{axiom | n = \text {II}
        | ml= \map \Pr \Omega
        | mo= =
        | mr= 1
}}
{{axiom | n = \text {III}
        | q = \forall A \in \Sigma
        | ml= \map \Pr A
        | mo= =
        | mr= \sum_{\bigcup \set e \mathop = A} \map \Pr {\set e}
        | rc= where $e$ denotes the elementary events of $\EE$
}}
{{end-axiom}}
\end{definition}