Sell, William. "Other Tracks"
Summary: Two scientific assistants use a time machine to visit the past, and discover that they have changed the present.
Comments: First known story to theorize that changing the past will alter the time-traveler's home time. However, subsequent historical development is minimal.
Published: In Astounding, October 1938; and Science Fiction Adventures in Dimensions (ed. Groff Conklin), Vanguard 1953, Berkley 1965.
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