Complex sentence: It is the first book of the Zarathustra Refugee Planets series; the other books are "Castaways' World" (1963) and "The Repairmen of Cyclops" (1965).
Split into simpler sentences: It is the first book of the Zarathustra Refugee Planets series. The other books are "Castaways' World" (1963) and "The Repairmen of Cyclops" (1965).