{

using type = static_combined_check_t<static_check_t<is_expression_t<Expr>::value, assert_on_is_expression_t>,

static_check_t<is_boolean_t<Expr>::value, assert_on_is_boolean_expression_t>>;

{

using _traits = make_traits<no_value_t, tag::is_on>;

using _nodes = detail::type_vector<Expression>;

Expression _expression;