I started to study ZFC axioms recently, here the intersection of a set S is defined as ⋂A={x:∀y(y∈A→x∈y)} , Thus if S = {{1, 2, 3}, {2, 3, 4}} then ⋂s = {2, 3}, then by this definition what would be ⋂S for a set where S = {1,2,3} , would it be same as S or the empty set.