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)
I dont see a use case for the Del operator, except in the vectorial expressions as shown in the unit tests. Once <code>CoordSysRect</code> comes in, each coordinate system will have a <code>Del</code> instance of its one. It could be accessed using <code>system.delop</code> . Each system's <code>delop</code> will differentiate wrt the base scalars assigned to that particular system.
Could you give an example of what you mean by an unevaluated form?