Maple ordinarily uses a three valued logic using the boolean values true, false, and FAIL. The Maple type boolean describes this set of values.

The type truefalse refers to only the two Boolean values true and false.

The expression type(e,'truefalse') evaluates to true if, and only if, the expression e is of type truefalse, which is defined as follows. The only two expressions that are of type truefalse are the expressions true and false. No other expression is of type truefalse.

Note that every expression that is of type truefalse is also of type boolean, but that the converse is not true. The value FAIL is not of type truefalse.

type( proc() true; end proc, 'truefalse' );