FOM: straification

[Vaughan Pratt]

From: Thomas Forster <T.Forster at dpmms.cam.ac.uk>
>A minor detail: i gathered from Marco Forti that the idea of a model
>of set theory as a set of atoms with an injection into its power set
>is due to his mentor di Giorgi.

Since this is exactly equivalent to extensionality, I would have thought
it was due to whoever first required extensionality.

If we had to keep track of every trivial rephrasing of axioms, textbooks
would be twice as thick.

Vaughan Pratt