Class

Proper class

A proper class is a Class which is not the element of any other class, and therefore not a set. If elementhood is defined by

𝔈⁡(𝑥)def⟺(∃ℭ𝔩𝔰⁡𝑦)[𝑥∈𝑦]

then a proper class 𝐴 satisfies ¬𝔈⁡(𝐴).

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