\begin{definition}[Definition:Probability Measure/Definition 4]
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 an additive function $\Pr: \Sigma \to \R$ which fulfils the following axioms:
{{begin-axiom}}
{{axiom | n = 1
        | q = \forall A, B \in \Sigma: A \cap B = \O
        | ml= \map \Pr {A \cup B}
        | mo= =
        | mr= \map \Pr A + \map \Pr B
}}
{{axiom | n = 2
        | ml= \map \Pr \Omega
        | mo= =
        | mr= 1
}}
{{end-axiom}}
\end{definition}