The eyereach of anaphora resolution

Before today I thought the anaphora resolution was hot research point with only lots of papers. However, when I read Anaphora Resolution: the state of art, Mitkov recommanded a primer Graham Hirst's book "Anaphora in natural language processing". I searched this by Google. And the result shook me up. There were more than one hundred books about anaphora. The earilest book about anaphora was Benveniste, E. «L'anaphorique prussien din et le système des démonstratifs IE», Studi baltici 3: 121-130.

It seemed that the books I could read about anaphora were more and more.