# New PDF release: Borel Liftings of Borel Sets: Some Decidable and Undecidable

By Gabriel Debs

ISBN-10: 0821839713

ISBN-13: 9780821839713

One of many goals of this paintings is to enquire a few traditional homes of Borel units that are undecidable in $ZFC$. The authors' place to begin is the subsequent straightforward, even though non-trivial consequence: examine $X \subset 2omega\times2omega$, set $Y=\pi(X)$, the place $\pi$ denotes the canonical projection of $2omega\times2omega$ onto the 1st issue, and believe that $(\star)$ : ""Any compact subset of $Y$ is the projection of a few compact subset of $X$"". If additionally $X$ is $\mathbf{\Pi zero 2$ then $(\star\star)$: ""The restrict of $\pi$ to a few rather closed subset of $X$ is ideal onto $Y$"" it follows that during the current case $Y$ can be $\mathbf{\Pi zero 2$. detect that the opposite implication $(\star\star)\Rightarrow(\star)$ holds trivially for any $X$ and $Y$. however the implication $(\star)\Rightarrow (\star\star)$ for an arbitrary Borel set $X \subset 2omega\times2omega$ is reminiscent of the assertion ""$\forall \alpha\in \omegaomega, \,\aleph 1$ is inaccessible in $L(\alpha)$"". extra exactly the authors turn out that the validity of $(\star)\Rightarrow(\star\star)$ for all $X \in \varSigma0 {1 \xi 1$, is similar to ""$\aleph \xi \aleph 1$"". besides the fact that we will convey independently, that after $X$ is Borel one could, in $ZFC$, derive from $(\star)$ the weaker end that $Y$ can also be Borel and of an analogous Baire type as $X$. This final end result solves an outdated challenge approximately compact masking mappings. in reality those effects are heavily regarding the subsequent common boundedness precept Lift$(X, Y)$: ""If any compact subset of $Y$ admits a continuing lifting in $X$, then $Y$ admits a continual lifting in $X$"", the place by way of a lifting of $Z\subset \pi(X)$ in $X$ we suggest a mapping on $Z$ whose graph is contained in $X$. the most results of this paintings will supply the precise set theoretical energy of this precept looking on the descriptive complexity of $X$ and $Y$. The authors additionally end up an analogous outcome for a edition of Lift$(X, Y)$ within which ""continuous liftings"" are changed by way of ""Borel liftings"", and which solutions a question of H. Friedman. between different purposes the authors receive a whole technique to an issue which fits again to Lusin about the lifestyles of $\mathbf{\Pi 1 1$ units with all ingredients in a few given type $\mathbf{\Gamma$ of Borel units, bettering past effects by way of J. Stern and R. Sami. The evidence of the most outcome will depend upon a nontrivial illustration of Borel units (in $ZFC$) of a brand new style, regarding a large number of ""abstract algebra"". This illustration was once at the beginning built for the needs of this evidence, yet has numerous different purposes.

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Additional resources for Borel Liftings of Borel Sets: Some Decidable and Undecidable Statements

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Then X(s/ u # ) = x(j / ) + x(@) - x (s/ n = Z ( ^ ) + x(7») ~ X(T(^ n Jf)) = xfJXst u #)) as desired. Apparently the definition for the Euler characteristic is internally consistent. 3 Evaluations for the Euler Characteristic The axiomatic approach provides a powerful scheme by which to determine values for Euler characteristics, as may be seen from some examples for some representative topological manifolds. AB] from point A at —1 on the x-axis to point B at 0 (on the x-axis) and the second [BC] from point B to point C at +1.

62, 219 (1989). 50. W. Thompson, Phil. , 34, 15 (1867). 51. E. G. , Kluwer, Dordrecht, 1991, p. 119. J. 1 Introduction......................................................................................... 3 Stoichiometry and Euler’s R elation.............................................. 4 Curvatures and G raph Em beddings.............................................. 5 Curvature Strain in M olecules....................................................... 6 O utlook.................................................................................................

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