NMLP P-026841 · True-first precedence · minted 2026-07-04

The Door into Summer

Robert A. Heinlein · Doubleday & Company, Garden City, NY · 1957

The US Doubleday hardcover is the true first, preceding the later UK Panther paperback. The first state shows 'First Edition' on the copyright page with no book-club gutter code.

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New Mexico Literacy Project — True-first precedence NMLP P-026841 for "The Door into Summer" by Robert A. Heinlein (https://newmexicoliteracyproject.org/id/point/p-026841, CC BY 4.0, dataset DOI 10.5281/zenodo.21184548).