We give a direct and very short proof of the famous Gibbard-Satterthwaite theorem [Alan Gibbard (1977) and Mark Satterthwaite (1975)]. The proof is based on investigating the properties of one critical preference profile constructed from those alternatives that individuals are not decisive on....

In a market with indivisibilities, Roth and Postlewaite (1977) show that the (weak) core can suffer from instability problems, in the sense that groups of individuals might upset the equilibrium by recontracting among themselves. By contrast, the strong core is stable. Following the seminal...