Here, a concept or idea - represented by the black dot, is being discussed in relationship with issues A and B. In Case 1, the concept is part of A and has no link to issue B, though A and B are linked together by overlap.

In Case 2, the concept is part of A, but since it is enclosed within B's circle, it has an influence on B. Case 3 shows the concept to be part of, and influencing both A and B.