[graph1_on_written_material
     [any written_material (^$(no inheritance)$^),
          may have for Coverage: a thing,
          may have for title: a string,
          may be object of: a publishing,
          result of: a writing,
          authoring_date: a time_measure,
          may have for author: a person,
          may have for Creator: a string,
          may be part of: a book,
          descr of: a situation,
          may have for Source: a document_element,
          may have for url: a URL]
];