I’ve never been a big Piers Anthony fan, so it might surprise some that I’m picking these up. But: A.) I have a long-term goal of picking up all the Gregg Press hardbacks, B.) I am given to understand that these (along with Macroscope and On A Pale Horse) are among his best work, and C.) They were incredibly cheap, $6 (plus bidder fee and shipping) for all three (plus a random Xanth novel) from a Heritage Auction.
See Hartwell, David G. “The GREGG PRESS Science Fiction Series 1975-1985 Complete, a Preliminary Annotated Checklist.”
These were the only volumes of the series done by Gregg Press. Volumes 4-6 were evidently done in hardcover by something called “Xlibris Corporation,” which I would guess is a Print-On-Demand publisher and lord, did they put some stupidly hideous covers on them…