Removal independence and multi-consensus functions
Work of Vincke and Bouyssou showed that if aggregation procedures on weak orders are allowed to return more than one result, then it might be possible for a procedure to satisfy all the axioms of Arrow's Theorem yet not be dictatorial. This approach is extended from ordered sets to n-trees, which are set-systems used in classifications theory. Results in this context can differ from those of Vincke and Bouyssou.