Four-Set Venn Diagram Game
This Demonstration shows a four-set Venn diagram. To be a Venn diagram, the graphics must be divided into 16 non-overlapping regions. All but one of the regions must be simply connected. A game consists of making a Venn diagram and dragging numbers to the right region. To play a game, press "reset". You can time yourself with the "start time" trigger.
Four-set diagram with ellipses was found by Venn [4, p. 43].
 F. Ruskey and M. Weston, "A Survey of Venn Diagrams," The Electronic Journal of Combinatorics, DS#5, 2005. www.combinatorics.org/files/Surveys/ds5/VennEJC.html.
 B. Grünbaum, "The Search for Symmetric Venn Diagrams," Geombinatorics, 8(4), 1999 pp. 104–109. (Jun 7, 2019) sites.math.washington.edu/~grunbaum/SymmetricVennDiagrams.pdf.
 Wikipedia. "Branko Grünbaum." (Jun 7, 2019) en.wikipedia.org/wiki/Branko_Gr%C3%BCnbaum.
 M. Gardner, Logic Machines, Diagrams and Boolean Algebra, New York: Dover Publications, 1968.