Venn Meets Boole in Symmetric ProofJanuary 13, 2004
Venn diagrams, long a staple of high school algebra, have also become a staple---or at least a paperclip -- for combinatorial geometers. The simplicity of the familiar two- and three-circle Venn diagrams turns out to be deceptive. Once a fourth set is added, circles no longer suffice and the subject raises a raft of challenging problems. One of them - the existence or non-existence of rotationally symmetric Venn diagrams -- was solved only recently.