Positive indiscernibles

Abstract

We generalise various theorems for finding indiscernible trees and arrays to positive logic: based on an existing modelling theorem for s-trees, we prove modelling theorems for str-trees, str${}_0$-trees (the reduct of str-trees that forgets the length comparison relation) and arrays. In doing so, we prove stronger versions for basing -- rather than locally basing or EM-basing -- str-trees on s-trees and str${}_0$-trees on str-trees. As an application we show that a thick positive theory has $k$-TP${}_2$ iff it has $2$-TP${}_2$.

17 pages