Class

Relation class

A relation class is a generalization of a Relation set. #m/def/set When working in a material set theory with classes, one may more widely consider a (binary) relation as any subset of the Cartesian product of classes where is the universal class, and we write

In a material set theory without classes like one may still treat this indirectly, by a predicative formula with two arguments. The Class existence theorem schema gives a sense in which these conceptions are equivalent in .

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