Glancing, Referring and Explaining in the Dialogue System HAM-RPM W Wahlster author A Jameson author W Hoeppner author 1978-12 text journal article American Journal of Computational Linguistics continuing periodical academic journal Microfiche 77 wahlster-etal-1978-glancing https://aclanthology.org/J78-3004/ 1978-12 53 67