Impredicative

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A mathematical definition is impredicative if it depends on a set of things, at least one of which is the thing which is itself being defined. In other words, the definition is self-referencing.

Russell's paradox is a famous example of an impredicative construction: the set of all sets which do not contain themselves. The paradox is whether such a set contains itself or not — if it does then by definition it should not, and if it does not then by definition it should.

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