Picking Representatives of Sets
Source: APMO 2014 Problem 2
March 28, 2014
induction
Problem Statement
Let . For each non-empty subset , one of its members is chosen as its representative. Find the number of ways to assign representatives to all non-empty subsets of so that if a subset is a disjoint union of non-empty subsets , then the representative of is also the representative of one of , , .Warut Suksompong, Thailand