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In their book "Theory of sets" Bourbaki suggested a general theory of isomorphism.

(See also http://www.tau.ac.il/~corry/publications/articles/pdf/bourbaki-structures.pdf )

The example of an untransportable relation (i.e. formula) in the book involves 2 principal base sets.

Are there examples of untrasportable formulas when we allow only one principal base set?

edited Jun 22 2010 at 13:40

asked Jun 19 2010 at 12:02

Victor Makarov
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Very few people here are familiar with Bourbaki's set theory. You should probably state the definitions here as well. – Harry Gindi Jun 19 2010 at 12:14

A reference is added in the question. – Victor Makarov Jun 22 2010 at 13:44

Victor Makarov · Accepted Answer · 2010-06-22 14:00:08Z UTC

An example of untrasportable sentence, when there is only one principal base set X, may be the following one:

All elements of the set X are finite sets,

Because, by definition, the truth value of a transportable sentence must be preserved under all bijections from the set X. Obviously, there exists a bijection from X to a set Y, where not all elements of Y are finite sets.

A simpler example is "the set X contains the empty set".

There is a paper "Sentences of type theory: the only sentences preserved under isomorphisms" by Victoria Marshall and Rolando Chuaqui - see The Journal of symbolic Logic, vol 56, #3, Sep 1991.

Bourbaki theory of isomorphism, examples of untransportable formulas

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