 Characteristic Classes by John Milnor and James D. Stasheff

Annals of Mathematics Studies 76, Princeton University Press. Academic scan: www.maths.ed.ac.uk/~v1ranick/papers/milnstas.pdf

Chapter 15, Theorem 15.3: the total Pontryagin class product formula holds modulo elements of order two. Verified against the original-text transcription in the TeXromancers edition: aareyanmanzoor.github.io/assets/books/characteristic-classes.pdf

The original scan exceeds the web extractor size limit; the theorem statement and proof were read in the retypeset original text. Locate by theorem number because the retypeset pagination differs.