Jost functions in the two-potential formalism

For two inhomogeneous Schrödinger equations playing an important role within the framework of the Gell-Mann — Goldberger two-potential formalism we derive the integral equations for the off-shell solutions and give the relations between the regular and Jost solutions. We define the Jost functions fully off the energy shell. The obtained formulae give the possibility to extend the validity of various useful relations derived within the one-potential theory.