Evelyn E. Smith's short story The Doorway was first published in the September 1955 edition of Fantastic Universe magazine.
The Doorway is a story of alternative time-lines and parallel universes.
Have you read it? What did you think?
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You can read this story for free through Project Gutenberg here: https://www.gutenberg.org/files/29138/29138-h/29138-h.htm