Entering partial derivatives?

[parisse]

The problem with | is an evaluation order problem and in addition a different meaning for the same variable name. At some point, when you are using a CAS, you have to understand that.
If you are using the HP50G in RPN mode, you have full control of evaluation, so it's easier to understand evaluation. But interaction is harder, especially doing again one computation with some modifications.
My point of view is that it's an error to expect students to use a math software without a minimum of explanations of the math teacher : you can sometimes hide difficulties but they are still there and they will bite later.
And it's not a loss of time to explain evaluation when using a CAS, to the contrary, it should be part of the math course!