OPTA was responsible for many French language publications in the 20th century. Mainly mystery and Science Fiction.
Both hardcover-books contain two SF-novels, and these are number 19 (Van Vogt) and 20 (Clarcke) from the series Club du livre d’antipation, both published in 1969.
Alfred Elton Van Vogt:
Au-delà du néant
/ Destination univers
Arthur Charles Clarcke: Les Enfants
d'Icare / La Cité et les astres