I cannot say anything about dirac_slash, thus here are some comments on the second topic:
"CD" == Chris Dams <Chris.Dams@mi.infn.it> writes: CD> (2) Why does the metric have indices?
It will be nice to combine two things: (a) to standardise storage of metric to an object of certain type; (b) to have a freedom to define metric from many different objects like matrices or tensors. Thus indexed object is chosen as a standard storage for a metric with its first component to hold actual metric (e.g. matrix or tensor). Indices are indeed somehow superficial but having some default values for them seems to be useful for example in same_metric(). Best wishes, Vladimir -- Vladimir V. Kisil email: kisilv@maths.leeds.ac.uk -- www: http://maths.leeds.ac.uk/~kisilv/