Ross, Sheldon. «Section 2.3. Axioms of Probability». A: A First Course in Probability ( PDF). 8a edició. Pearson Prentice Hall, 2010, p. 26–27. ISBN 978-0-13-603313-4 [Consulta: 22 agost 2016]. «(anglès)Axiom 3.
For any sequence of mutually exclusive events (that is, events for which when ),
[...] Axiom 3 states that, for any
sequence of mutually exclusive events, the probability of at least one of these events
occurring is just the sum of their respective probabilities.»