...effect

Usually, assigning Undefined to a variable will also result in a run-time error.

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...{}.

This is already the case for subrange types in most languages. The argument here is that it should apply to other types as well.

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...values

If $U$ is treated as a value, it becomes possible to specify paradoxical sets, for example . To avoid paradoxes we decree that $U\; \in U$ and $U\; \subset U$ by definition and that all paradoxical set formers must result in Undefined.

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