Back Axioma d'extensionalitat Catalan Extensionalitätsaxiom German Αξίωμα της επεκτασιμότητας Greek Axioma de extensionalidad Spanish Ekstensionaalsuse aksioom Estonian اصل موضوع هممصداقی Persian Axiome d'extensionnalité French אקסיומת ההיקפיות HE Aksiom rasprostranjenosti Croatian Extenzionalitási axióma Hungarian
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (March 2013) |
In axiomatic set theory and the branches of logic, mathematics, and computer science which rely upon it, the axiom of extensionality is one of the axioms of Zermelo–Fraenkel set theory. Informally, the axiom means that the two sets A and B are equal if and only if A and B have the same members.