sau'au VUhU3 experimental cmavo

mekso binary operator: del, nabla, quabla, partial-derivative vector/tensor operator; outputs the functional-valued formal-covector (or analog thereof) of partial derivatives with respect to X1 (tensor in the same format and order), each degree X2 (default: 1).

Suitable assumption or specification of dimensionality, a suitable differentiation order, a suitable metric, and a sufficiently differentiable function are required. X1 may be assumed according to context. Potentially combine with, for example, the cross-prpduct operator for curl. See: "sa'o".