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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.

15 votes
0 answers
237 views

Natural examples of Borel surjections without right inverse

As discussed in this question, in general a Borel surjection $f:\mathbb{R}\rightarrow\mathbb{R}$ may not have a Borel right inverse, namely a $g$ such that $f\circ g=id$, although there is always a co …
183orbco3's user avatar
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13 votes
1 answer
266 views

Descriptive complexity of analytic continuation

Consider the set of complex power series $$ f(z)=\sum_{n=0}^\infty a_nz^n $$ that have radius of convergence $1$ and can be analytically continued to the neighborhood of some point on the unit circle. …
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0 votes

Some "axiom of choice" and "dependent choice" issues

The answer to (2) actually depends on the exact meaning of "strictly larger", since cardinalities without choice are a mess. Working in ZF+DC, if $\mathcal{B}$ is a countably generated $\sigma$-algebr …
183orbco3's user avatar
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