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If you see a formula in the Physical Review that extends over a quarter of a page, forget it. It's wrong. Nature isn't that complicated.
Benedetto da Firenze's Trattato d'arismetriche
Benedetto da Firenze (1429 – 1479) was a respected Florentine maestro d’abaco. Here, on page 114 of his unpublished manuscript Trattato d’arismetricha (ca 1460), a work on mercantile arithmetic, is a discussion of regula del chataina, the chain rule, used to compute exchange rates.