Issues with partial derivatives ?

The grader seems not to understand partial derivatives correctly. For instance:


This may be due to the ``\delta`` symbol interpretation by the sympy parser.

Start by reproducing the partial-derivative example shown in the issue and inspect how the SymPy parser interprets the delta symbol. No repository file or test is named; done means identifying the parsing failure and demonstrating that the grader correctly evaluates the reported partial-derivative answer.

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