Definition:Probability/Formal Definition

Probability
Let $\EE$ be an experiment.

Let $A \in \Sigma$ be an event in the event space $\Sigma$ of $\EE$.

Let $\Pr$ be the probability measure of $\EE$.

Then the probability of $A$ is the value $\map \Pr A$.

Also denoted as
Some sources give the probability of $A$ as $\map P A$