Envy-free division in the presence of a dragon

Abstract

We prove several results addressing the envy-free division problem in the presence of an unpredictable (secretive) player, called the "dragon". There are two basic scenarios. 1. There are $r-1$ players and a dragon. Once the "cake" is divided into $r$ parts, the dragon makes his choice and grabs one of the pieces. After that the players want to divide the remaining pieces in an envy-free fashion. 2. There are $r+1$ players who divide the cake into $r$ pieces. A ferocious dragon comes and swallows one of the players. The players want to cut the cake in advance in such a way that no matter who is the unlucky player swallowed by the dragon, the remaining players can share the tiles in an envy-free manner. In both settings the players are allowed to choose degenerate pieces of the cake. Moreover, they construct in advance both a cut of the cake and a "decision tree", allowing them to minimize the uncertainty of what pieces can be given to each of the players.

The presentation is improved and a proof of the "Dragon marriage lemma" (Section 1.2) is included