Possible Clues:

• -- diagram, one with overlapping circles
• -- diagram (math image)
• -- diagram (logic tool)
• Diagram style with overlap
• John who was a pioneer in set theory
• Logician known for overlapping diagrams
• Diagram variety with overlap
• — diagram (logic image)
• Logician John, for whom overlapping-circle diagrams are named
• ___ diagram (infographic with overlapping circles)