[chobytes]

There is a general notion of derivations I believe theyre using. Ie anything that obeys the Leibniz rule (fg)' = f'g+fh'.

Its an informative exercise to see how many of the standard rules of calculus can be derived using just this rule.

[patrickthebold]

https://en.wikipedia.org/wiki/Derivation_(differential_algeb... is probably what you were referring to.