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The Quine pair works in ordinary set theory (Zermelo or ZFC); it has a mildly baroque definition but there is no problem with it. Look at the machinery and you
by randallholmes 2y ago
The Quine pair works in ordinary set theory (Zermelo or ZFC); it has a mildly baroque definition but there is no problem with it. Look at the machinery and you will see why a pair (as opposed to a general set) doesnt strictly speaking need to be of higher type than its components.