N-Space

``What Can You Say About Chocolate Covered Manhole Covers?'' or, indeed, about any of the provocative ideas that Niven ( Ringworld ) raises in this retrospective collection ranging over three decades of work. This bemusingly titled story is one answer to the question: Why is nobody out there talking to us? ``Bordered in Black'' provides a second answer, and ``The Fourth Profession'' a third. ``Madness Has Its Place'' is a missing tale from the Known Space series, while ``Down in Flames'' gives the outline for a story in which all Known Space is destroyed. ``Brenda'' is a novella featuring the Sauron Superman described in Mote; it is nicely complemented by ``Building The Mote in God's Eye. '' In ``The Return of William Proxmire'' the title character uses a time machine to save the health and military career of Robert A. Heinlein. While some of the stories here are classics, most have not previously been collected in book form. Niven's essays on the SF genre and commentaries on the stories make this collection a must for SF fans. (Sept.)