If x is a reasonable agreement in a game V , then so should it remain in the associated game Vx where the coalitions can buy up the cooperation of non-members by 'paying' them according to x. This new stability property called 'Invariance with respect to re-evaluations of coalitional power' (IRCP) allows to characterize the core as the largest solution specifying feasible allocations that are individually rational. In addition, a natural adaptation of IRCP allows to elegantly characterize the inner core for NTU games with convex and smooth feasible sets.
De Clippel, G. (2003). Invariance with respect to re-evaluations of coalitional power (ECON Discussion Papers 2003/56). https://hdl.handle.net/2078.5/38258