A note on the NFI-topology

Abstract

The $NFI$-topology, introduced in [S0], is a topology on the Stone space of a theory $T$ that depends on a reduct $T^{-}$ of $T$. This topology has been used in [S0] to describe the set of universal transducers for $(T,T^{-})$ (invariants sets that translates forking-open sets in $T^{-}$ to forking-open sets in $T$). In this paper we show that in contrast to the stable case, the $NFI$-topology need not be invariant over parameters in $T^{-}$ but a weak version of this holds for any simple $T$. We also note that for the lovely pair expansions, of theories with the \em wnfcp\em , the topology is invariant over $\varnothing$ in $T^{-}$.