Formally, this can be cast as a combinatorial domain where the set of binary issues is X ={X 1 ,...,X p }, with D i ={0 i , 1 i } for each i. These binary issues correspond to a set of items C ={c 1 ,...,c p }, where X i = 1 i (resp. 0 i ) means that item c i is (resp. is not) in the selection S. Because of the focus on the selection of a subset of items, we change the notational convention by denoting an alternative x ∈ A = {0 1 , 1 1 }×...×{0 p , 1 p } as a subset of issues S composed of items c i s with X i = 1 i . Thus, alternatives are elements of 2 C .