the set itself.

Theories of universality

The difficulties associated with a universal set can be avoided either by using a variant of set theory in which the axiom of comprehension is restricted in some way, or by using a universal object that is not considered to be a set.

Restricted comprehension

There are set theories known to be consistent (if the usual set theory is consistent) in which the universal set does exist (and is true). In these theories, Zermelo's axiom of comprehension

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