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boolean operators
Not E
E And F
E Or F
where E and F are of type BOOL.

These operators have their usual meanings. Note that when two or more
boolean expressions are combined with AND, they are evaluated one by
one until a FALSE expression is found. The rest are not evaluated.
For example, given the expression
A And B, the system does not
attempt to evaluate B unless A evaluates to TRUE. Similarly,
evaluation of a sequence of boolean expressions connected by OR stops
as soon as a TRUE expression is found.