Basic vector code, without a coordinate system class

All calculations essentially occur in the same frame.
i, j, k and x, y, z are imported as base vectors and base scalars by default on importing sympy.vector.
delop is a Del operator instance.

Example:

>>> v = 3*i - j
>>> delop ^ v
0

(delop ^ v represents curl of v)
Please ask about this on the SymPy email list. Integral, Limit, Derivative, Series, etc all seem to have unevaluated classes and then a function to do the evaluation. To me, Del seems like a very similar case.