\documentclass[a4paper]{article} \usepackage{amssymb} \pagestyle{empty} \hoffset=-40pt \voffset=-20pt \textwidth 15.3cm \textheight 22cm % to fit our printers \begin{document} \begin{center}{\huge Nonisolated Regular Types in Superstable Theories}\end{center} \begin{center}{\large Predrag Tanovic\\Matematicki Institut SANU\\Knez Mihajlova 35, Beograd}\end{center} \bigskip \large Let $T$ be a countable, superstable theory and ${\cal M}$ its monster model. \bigskip \noindent{\bf Definition} Let $p \in S(A)$ be nonalgebraic. \begin{enumerate} \item[{(a)}] $p$ is strongly nonisolated if for all finite $B$ and all formulas $\varphi(\overline x)$ over $AB$ consistent with $T$, there exists $q \in [\varphi]_{AB}$ such that $p \bot^aq$. \smallskip \item[{(b)}] $p$ is eventually strongly nonisolated, or ${\rm esn}$ for short, if there is a finite set $B$ and $a$ nonforking extension $q \in S(AB)$ which is strongly nonisolated. \end{enumerate} We discuss the following: \medskip \noindent{\bf Theorem} Suppose $p \in S(\emptyset)$ is regular, stationary and has limit ordinal $U$-rank. The following are all equivalent: \begin{enumerate} \item[{(I)}] $p$ is eventually strongly nonisolated; \smallskip \item[{(II)}] There is an integer $n$ such that for no formula $\varphi(x_1,x_2,\dots,x_n)$ we have: \smallskip $$ (\varphi(x_1,x_2,\dots,x_n) \wedge p(x_1) \wedge p(x_2)\wedge\dots\wedge p(x_n)) \Leftrightarrow p^n(x_1,x_2,\dots,x_n)\,; $$ \item[{(III)}] There exists a finite set $A$ and a sequence $\{q_n\mid n\odot \omega\}$ of types extending $p$ to $S(A)$ such that $$ bnd(q_0) < bnd(q_1) <\, \dots \,< bnd(q_n) < bnd(q_{n+1}) <\,\dots\quad\mbox{and}\quad \lim_{n\to\infty}bnd(q_n) = bnd(p)\,. $$ \end{enumerate} \end{document}