The first sign of senility is that a man forgets his theorems, the second sign is that he forgets to zip up, the third sign is that he forgets to zip down.

Notes from Wikiquote

This has also been attributed, with variants, to Paul Erdős, who repeated the remark.

Adventures of a Mathematician - Third Edition (1991)

Adventures of a Mathematician - Third Edition (1991)

Adventures of a Mathematician - Third Edition (1991)

Adventures of a Mathematician - Third Edition (1991)

Quote text and notes from Wikiquote: Stanislaw Ulam (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.