From Wikipedia: https://en.wikipedia.org/wiki/Derivative
The dy/dx notation is from Leibniz. Note that the y term is usually on top.
The ' (or prime) notation is from Lagrange. Both notations are in common use.
I don't understand you question about an "inverse function."
>> JS
Comments and follow-on questions should be posted here not in personal messages.
We can not see the context for the disagreement between you and your colleague.
What is the specific question that caused the disagreement, and what are the competing answers?
I have already noted that your expression is flipped from the usual form of the 2nd derivative: (d²y)/(dx²) <== Why do you think that this form is inadeqauate?
The questions remains unclear, but BigRat's answer is comprehensive.
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From Wikipedia: https://en.wikipedia.org/wiki/Derivative
The dy/dx notation is from Leibniz. Note that the y term is usually on top.
The ' (or prime) notation is from Lagrange. Both notations are in common use.
I don't understand you question about an "inverse function."