On NIP and invariant measures
Abstract
Description
We study forking, Lascar strong types, Keisler measures and definable groups, under an assumption of $NIP$ (not the independence property), continuing aspects of math.LO/0607442. Among key results are: (i) if $p = tp(b/A)$ does not fork over $A$ then the Lascar strong type of $b$ over $A$ coincides with the compact strong type of $b$ over $A$ and any global nonforking extension of $p$ is Borel definable over $bdd(A)$ (ii) analogous statements for Keisler measures and definable groups, including the fact that $G^{000} = G^{00}$ for $G$ definably amenable, (iii) definitions, characterizations and properties of "generically stable" types and groups (iv) uniqueness of translation invariant Keisler measures on groups with finitely satisfiable generics (vi) A proof of the compact domination conjecture for definably compact commutative groups in $o$-minimal expansions of real closed fields.
Changes from the first version include removing the old section 8 on generic compact domination, giving a more complete account of the Vapnik-Chervonenkis theorem and its applications, the addition of an appendix on the existence of definable Skolem functions in suitable o-minimal structures, as well as expanding and clarifying various proofs
Changes from the first version include removing the old section 8 on generic compact domination, giving a more complete account of the Vapnik-Chervonenkis theorem and its applications, the addition of an appendix on the existence of definable Skolem functions in suitable o-minimal structures, as well as expanding and clarifying various proofs