Objects of type boolean represent truth values. The boolean constants are TRUE and FALSE; the most important operations on boolean values are and (logical conjunction), or (logic disjunction), and not (negation). In expressions, not binds stronger than and, which in turn binds stronger than or. The most important usage of boolean expressions is for conditions in control constructs, like if, while, or loop.
Example:
> work:=FALSE
> island:=TRUE
> work and island
Result= FALSE
> work or island
Result= TRUE
> not work and island
Result= TRUE
See also: and, or, not, Operators and Expressions.