This program displays Venn diagrams. Expressions are
constructed from the sets, A, B, C, S (universal set), and E (empty
set), and the four operations, U (union), ^ (intersection),  (relative
complement), and ' (complement). There are two games in this program:
find the number, and find the region. The user can ask questions,
using set notation, to obtain clues as to what the number or region
is.Sample expressions are provided.
