The possibility to define natural number multiplication in the language $L(+,2^{(\cdot)})$ makes that theory undecidable.
What about is the complexity of the theory of addition (Presburger arithmetic) augmented by a unary predicate that recognizes powers of 2?
Side question: does anyone know terse unsolved problems shorter to state in the language $L(+,2^{(\cdot)})$ than in $L(+,\times)$?

