I think that may be the first time that has ever been written (not least because Leibniz was no model of rigour …).
Leibniz of course turned out to be right (or had the right intuition) but he failed to provide rigorous definitions of limits, functions, etc.
I only made the connection as some models of assignment I've seen use a rule of syntactic substitution from Leibniz in the method of proof.
Rigorous if you're a programmer not used to using proofs.
I think that may be the first time that has ever been written (not least because Leibniz was no model of rigour …).