• The book that taught mathematicians how to guess before they prove: Polya on plausible reasoning, complete in both 1954 Princeton volumes with jackets, and still assigned seventy years on, which is decent inductive evidence for its own thesis
• Volume I Induction and Analogy in Mathematics. Volume II Patterns of Plausible Inference. Princeton University Press, 1954 on both title pages, issued at $5.50 and $4.50 separately or $9.00 the set, exactly as printed on this set's own jacket flaps
• The companion to How to Solve It and the deeper of the two, arguing that mathematical discovery runs on plausible reasoning long before rigorous proof arrives to tidy it up
• A dating detail found on the books themselves: both rear jacket flaps advertise The Enjoyment of Mathematics by Rademacher and Toeplitz, which Princeton published in 1957, so the jackets came from a later run than the 1954 text they cover
• Volume II carries a handwritten period ownership name on the front endpaper. Sold as photographed, with jackets present on both volumes

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