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Some are empty, set up at the crack of dawn and then abandoned for hours on end, until the owners actually want to use them.

Other examples are the axiom of the empty set, which states that a set without elements exists, and the axiom of pairing, according to which two sets with the same elements are equal.

It would almost be easier to make a list of topics he didn't lie about, except for the very real threat it would be an empty set.

After all, work in this field is based on a few basic assumptions that are as simple as possible—such as that there is an empty set—from which results as complicated as Gödel's incompleteness theorems can be inferred.

Meanwhile the camera panned to an empty set.