Conservative extensions of models with weakly o-minimal theories
B. S. Baizhanov Institute for Problems of Informatics and Control Sciences, Almaty
Abstract:
Let
$M\prec N$. It is said that a pair of models
$(M,N)$ is conservative pair and
$N$ is conservative extension of
$M$ if for any finite tuple of elements
$\overline{\alpha}$ from
$N$,
$\mathrm{tp}(\overline{\alpha}|M)$ is definable. We say that elementary extension
$N$ of
$M$ is
$D$-good if any definable
$q\in S(M\cup\overline{\alpha})$ (
$\overline{\alpha}\in N\setminus M$) is realized in
$N$ and
$N$ is
$CD$-good if any non-isolated one-type
$q\in S_1(M\cup\overline{\alpha})$ (
$\overline{\alpha}\in N\setminus M$), which is determined (approximated) by definable
$\phi$-type, is realized in
$N$.
We prove that any model
$M$ of any weakly o-minimal theory except one, theory of discrete order with ends, has conservative extension. The central point in our paper is the criterion of the existence of the
$CD$-
$\omega$-saturated conservative extension of an arbitrary model of weakly o-minimal theory (Theorem 2). As corollary of this proof it follows the existence of
$CD$-
$\omega$-saturated conservative extension for any model of any weakly o-minimal theory except one and the results on omitting of natural family of definable one-types and all non-definable types (Corollary 5). The existence of conservative and
$CD$-
$\omega$-saturated conservative extensions for o-minimal theories have been proved accordingly in
D. Marker, “Omitting types in o-minimal theories”,
The Journal of Symbolic Logic, Vol. 51(1986), P. 63–74.,
Y. Baisalov, B. Poizat, “Paires de structures o-minimales”,
The Journal of Symbolic Logic, Vol. 63(1998), P. 570–578.
UDC:
510.67 Received: 30.04.2003