World's Best Science Fiction, First Series 91354 SF Donald A. Wollheim and Terry Carr (eds.) World's Best Science Fiction, Second Series 91355 SF Donald A. Wollheim and Terry Carr (eds.) World's Best Science Fiction, Third Series 91356 SF Donald A. Wollheim and Terry Carr (eds.) World's Best Science Fiction, Fourth Series 91357 SF Donald A. Wollheim and Terry Carr (eds.) World's Best Science Fiction, 1970 91358 SF Donald A. Wollheim and Terry Carr (eds.) World's Best Science Fiction, 1971 91359 SF Frederik Pohl Best SF for 1972 91502 SF Robert A. Heinlein The Worlds of Robert A. Heinlein (1973) 91581 SF Keith Laumer Worlds of the Imperium 91640 SF Fritz Leiber The Worlds of Fritz Leiber 91706 SF Poul Anderson World Without Stars 91770 SF Robert E. Howard Worms of the Earth 92551 SF Andre Norton The X Factor 92553 SF Andre Norton The X Factor 94200 SF Wilson Tucker The Year of the Quiet Sun (1970) 94251 SF Andre Norton Year of the Unicorn 94254 SF Andre Norton Year of the Unicorn (1979) 95490 SF Andre Norton Zarsthor's Bane (1978) 95941 SF Andre Norton Zarsthor's Bane 95960 SF Andre Norton The Zero Stone 95961 SF Andre Norton The Zero Stone 95964 SF Andre Norton The Zero Stone (1981) References Ace Image Library. Contains images of most covers for both the singles and doubles. Tuck, Donald H. The Encyclopedia of Science Fiction and Fantasy: Volume 3'', Advent: Publishers, Inc., 1982. . Lists all ACE sf titles, single and double, published through 1968. Ace SF numeric-series single titles SF numeric-series single titles Ace SF numeric-series single titles