Chain Rule

Any differential divided by itself is one.

$\dfrac {du}{dz} = \dfrac {du}{dw} \dfrac {dw}{dx} \dfrac {dx}{dy}\dfrac {dy}{dz}$

Can you see the cancellations for dw, dx and dy?

It is typical for a problem in Calculus I to make use of the following:

$\dfrac {df}{dx} = \dfrac {df}{du} \dfrac {du}{dx}$

Appendix A

The Chain Rule carries (hides?) the idea of local flatness.