Characterizations of interpretability in bounded arithmetic
  This paper deals with three tools to compare proof-theoretic strength of formal arithmetical theories: interpretability, $\Pi^0_1$-conservativity and proving restricted consistency. It is well known that under certain conditions these three notions are equivalent and this equivalence is often referred to as the Orey-H\'ajek characterization of interpretability.   In this paper we look with detail at the Orey-H\'ajek characterization and study what conditions are needed and in what meta-theory the characterizations can be formalized. 
Joost J. Joosten
math.LO