An elementary theory of concatenation, QT + , is introduced and used to establish mutual interpretability of Robinson arithmetic, Minimal Predicative Set Theory, quantifier-free part of Kirby's finitary set theory, and Adjunctive Set Theory, with or without extensionality.] arithmetical laws. Additionally, an impressive amount of non-trivial mathematics can be reconstructed in theories interpretable in Q, including (first-order) Euclidean geometry, elementary theory of the real closed fields (i.e., first-order theory of real numbers) as well as basic "feasible analysis" formalizing elementary properties of real numbers and continuous functions.(See [4] for details.) It is frequently pointed out that Q is a minimal element in the well-ordered hierarchy of interpretability of "natural" mathematical theories.It was Tarski who first noted that, as regards self-referential constructions at the heart of meta-mathematical arguments for incompleteness, the procedure of arithmetization by means of which the syntax of formal theories is coded up by numbers amounts to an unnecessary detour. In his seminal work on the concept of truth of formalized languages Tarski introduced a theory of concatenated strings to demonstrate this point. This idea was further developed by Quine [13]. More recently, Grzegorczyk has suggested that a theory of concatenated "texts" would form a natural framework for the study of incompleteness phenomena and, more generally, computation, and for this purpose he introduced a weak theory of concatenation, TC, and proved its