20 Booleans

The two main boolean values are true and false. They stand for the logical values of the same name. They appear as values of the conditions in if-statements and while-loops. Booleans are also important as return values of filters (see Filters) such as IsFinite and IsBool. Note that it is a convention that the name of a function that returns true or false according to the outcome, starts with Is.

For technical reasons, also the value fail (see Fail) is regarded as a boolean.

gap> IsBool( true );  IsBool( false );  IsBool( 17 );
true
true
false