db/conf/ht/Engebretsen97.html Martin Engebretsen Hyper-news: Revolution or Contradiction? 222-223 HT1997/P222.pdf 1997 conf/ht/97 Hypertext db/conf/ht/ht97.html#Engebretsen97 http://doi.acm.org/10.1145/267437.267469