The following is a Venn diagram for 4 sets: In the diagram, the first set is labeled "A", and it contains all sets in which "A" is a member. The second set is labeled "B", and it contains all sets in which "B" is a member. The third set is labeled "C", and it contains all sets in which "C" is a member. Finally, the fourth set is labeled "D". This set contains all sets in which both of the other two sets are members.