Bondareva–Shapley theorem

The Bondareva–Shapley theorem, in game theory, describes a necessary and sufficient condition for the non-emptiness of the core of a cooperative game in characteristic function form. Specifically, the game's core is non-empty if and only if the game is balanced. The Bondareva–Shapley theorem implies that market games and convex games have non-empty cores. The theorem was formulated independently by Olga Bondareva and Lloyd Shapley in the 1960s.

Theorem

Let the pair ${\displaystyle \langle N,v\rangle }$ be a cooperative game in characteristic function form, where ${\displaystyle N;}$ is the set of players and where the value function ${\displaystyle v:2^{N}\to \mathbb {R} }$ is defined on ${\displaystyle N}$'s power set (the set of all subsets of ${\displaystyle N}$).

The core of ${\displaystyle \langle N,v\rangle }$ is non-empty if and only if for every function ${\displaystyle \alpha :2^{N}\setminus \{\emptyset \}\to [0,1]}$ where

${\displaystyle \forall i\in N:\sum _{S\in 2^{N}:\;i\in S}\alpha (S)=1}$
the following condition holds:

${\displaystyle \sum _{S\in 2^{N}\setminus \{\emptyset \}}\alpha (S)v(S)\leq v(N).}$