\begin{definition}[Definition:Event/Occurrence/Equality]
Let the probability space of an experiment $\EE$ be $\struct {\Omega, \Sigma, \Pr}$.
Let $A, B \in \Sigma$ be events of $\EE$ such that $A = B$.
Then:
:the occurrence of $A$ inevitably brings about the occurrence of $B$
and:
:the occurrence of $B$ inevitably brings about the occurrence of $A$.
\end{definition}