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first-order and higher-order logic, model theory, set theory, proof theory, computability theory, formal languages, definability, interplay of syntax and semantics, constructive logic, intuitionism, philosophical logic, modal logic, completeness, Gödel incompleteness, decidability, undecidability, theories of truth, truth revision, consistency.

3 votes
1 answer
78 views

Can one say that there are equal numbers of sets satisfying formulas in Second Order Arithme...

Is there a way of saying in second order arithmetic that the number of sets $X$ such that $\phi$ equals the number of sets $X$ such that $\psi$, where $\phi$ and $\psi$ are formulas with $X$ free, and …
Alexander Pruss's user avatar
6 votes
1 answer
223 views

Can one define second-order equinumerosity in MSO via first-order cardinality quantifiers?

Let $L$ be MSO (Monadic Second Order Logic) extended with an $n$-ary second-order cardinality predicate (i.e., a first-order cardinality quantifier) $C_R$ for every $n$-ary relation $R$ on the natural …
Alexander Pruss's user avatar