We introduce the oak property of first order theories, which is a syntactical condition that we show to be sufficient for a theory not to have universal models in cardinality whe...
This paper continues [Sh500] and [DzSh692]. We present a rank function for NSOP1 theories and give an example of a theory which is NSOP1 but not simple. We also investigate the con...
In this paper we study the idea of theories with containers, like sets, pairs, sequences. We provide a modest framework to study such theories. We prove two concrete results. Firs...
We show the non-arithmeticity of 1st order theories of lattices of n sentences modulo provable equivalence in a formal theory, of diagonalizable algebras of a wider class of arithm...
We show that the first order theories of the Medevdev lattice and the Muchnik lattice are both computably isomorphic to the third order theory of the natural numbers.