Description of the illustration boolean_expression.eps

[ NOT ] { boolean_constant
        | boolean_function_call
        | boolean_literal
        | boolean_variable
        | conditional_predicate
        | other_boolean_form
        }
        [ { AND | OR } [ NOT ] { boolean_constant
                               | boolean_function_call
                               | boolean_literal
                               | boolean_variable
                               | conditional_predicate
                               | other_boolean_form
                               }
        ]...