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Mathematical logic, Set theory, Peano arithmetic, Model theory, Proof theory, Recursion theory, Computability theory, Univalent foundations, Reverse mathematics, Frege foundation of arithmetic, Goedel's incompleteness and Mathematics, Structural set theory, Category theory, Type theory.

3 votes

Applications of ZFA-Set Theory

Arnold Oberschelp used urelements in his relative consistency proof of a set theory with a universal set and the singleton function as a set. I followed his example in my variant of Alonzo Church’s “ …
Flash Sheridan's user avatar
2 votes

Anti-foundational set theory with a universal set

Check out the theory at the end of Vicious Circles by Barwise & Moss, which has the Universal Set U, though the “collection of all sets distinct from U will not be a class.” (p. 308). I crafted some …
Flash Sheridan's user avatar
5 votes

Where is the end of universe?

Have a look at Church’s (first) Set Theory with a Universal Set, which is equiconsistent with ZFGC, though Church didn’t publish a full proof, and I think he abandoned the proof in his archives at Pri …
Flash Sheridan's user avatar
3 votes

Set theory and alternative foundations

To follow up further on Joel David Hamkins's answer on geometry, Frege’s last work (two despairing decades after Russell’s Paradox demolished his Grundgesetze der Arithmetik) was a brief unpublished p …
Flash Sheridan's user avatar