Open Space published this lecture given by Robert Duncan at Dominican College in San Rafael on October 27, 1965 on the occasion of Dante's 700th birthday. I worked with a guy at the bookstore who was a huge Duncan fan. I just did not get it. That said I love The HD Book and felt it to be on par with other examples of creative criticism by William Carlos Williams, Susan Howe or Charles Olson.
Graham Mackintosh printed 500 copies of the lecture with wrappers illustrated by Duncan. I am going to go out on a limb and say this was not a popular title for Open Space/White Rabbit. There are currently 26 copies available on Abebooks, which makes it the rare book equivalent of a remainder.