I decided not to modify ```tensor.py``` 's code, when I subclassed, there were problems like loss of data. For example, I put a VTensorIndexType inside a VTensorHead(TensorHead), and the metric data in VTensorIndexType was stripped away.

Methods did return ```tensor``` objects instead of ```vtensor``` objects, and all data kept being converted from ```VT-objects``` to ```T-objects```, so I gave up subclassing.