public function delete_category($categoryid) {
        global $CFG, $DB;
        question_can_delete_cat($categoryid);
        if (!$category = $DB->get_record("question_categories", array("id" => $categoryid))) {  // security
            print_error('unknowcategory');
        }
        /// Send the children categories to live with their grandparent
        $DB->set_field("question_categories", "parent", $category->parent, array("parent" => $category->id));

        /// Finally delete the category itself
        $DB->delete_records("question_categories", array("id" => $category->id));

        // Log the deletion of this category.
        $event = \core\event\question_category_deleted::create_from_question_category_instance($category);
        $event->add_record_snapshot('question_categories', $category);
        $event->trigger();

    }