Core Convergence
Robert M. Anderson · The New Palgrave Dictionary of Economics · 2008
The core of an economy, first defined by Edgeworth (1881), is the set of all economic outcomes such that no group of individuals (‘coalition’) can make each of its members better off (‘improve on’ or ‘block’ the outcome), using only the resources available to the group. (A common mistake is to ask, in reference to a particular core allocation, ‘what coalition(s) have formed?’ An allocation is in the core precisely when no coalition can improve on it, and a core allocation does not identify an associated coalition or coalitions. It is when an allocation is not in the core that one can identify one or more coalitions that are associated with it, because they can improve on it and thus demonstrate that the coalition is not in the core.)