Mention the number of authors of the paper 'Groupware for realtime collaboration'.
The paper 'Groupware for realtime collaboration' has how many authors?
SELECT ?answer WHERE { <https://dblp.org/rec/conf/chi/HillB94> <https://dblp.org/rdf/schema#numberOfCreators> ?answer }
<https://dblp.org/rec/conf/chi/HillB94>