1.2.1 Venn Diagrams
Venn diagrams are very useful in visualizing relation between sets. In a Venn diagram any set is depicted by a closed region. Figure 1.2 shows an example of a Venn diagram. In this figure, the big rectangle shows the universal set $S$. The shaded area shows another set $A$.
Figure 1.3 shows two sets $A$ and $B$, where $B \subset A$.
