History of Space Exploration: Chapter 1, Exercise 2 — Possible Solution
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QUALIFICATION
The only independence the sources state is Goddard developing the rocket
equation around 1912, though Tsiolkovsky published earlier. The Oberth source
says nothing on originality, and I found nothing on whether the three knew each
other's work. None of them is said to have invented spaceflight.

REWRITE
"Tsiolkovsky, Goddard and Oberth each made major theoretical contributions;
Goddard is said to have developed the rocket equation independently."