Question: Problem aplying the chain rule with dchange

I have a problem using dchange when my variable depend on two (or more variables) and I would like to apply the chain rule.

For example, when I use the command

I would expect something like 

But I get an error saying that the number of new variables and transformation equations must be the same.

Any idea how I could solve it? 

Thanls a lot for your help.

 

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