We model a situation where a set of agents must rank themselves based on their opinions. Each agent submits a message and a function determines the social ranking. We are interested in impartial social ranking functions, that is, those where the message of an agent can not change any social...

We model a situation where a set of agents must rank themselves based on their opinions. Each agent submits a message and a function determines the social ranking. We are interested in impartial social ranking functions, that is, those where the message of an agent can not change any social...

Environments with semi-ordered preferences, which may exhibit indifference intransitivity, are known to allow just-noticeable differences in preference intensity to serve as interpersonally comparable units of utility. I prove two impossibility theorems for social choice in such environments....

We know that ex-post Pareto efficiency is possible with strategy-proofness and weak envy-freeness while ordinally efficiency is incompatible with them. We strengthen this impossibility for random assignments and show that it prevails if ordinal efficiency is weakened to robust ex-post Pareto...