Using FeynCalc in calculations with the spacetime dimension different from 4 or D

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This is a thread to exchange user experience in doing covariant calculations with D=3 or D=2,
i.e. when the spacetime dimension is not 4.

Notice that this different from nonrelativistic calculations (supported since FC 9.3) where the
spacetime dimension is still 4, but we treat spatial and temporal components separately.

An example of such calculation would be https://arxiv.org/pdf/hep-th/0305043.pdf

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Just some random thought son how this could be implemented in some future FC version

• All calculations must be done in D-dimenions, as the default dimension D=4 is not compatible with D=2|3
• Need to introduce special versions of LC and GA[5] that have properties compatible with D=2|3

Another idea would be to have a global switch that activates D=2|3 before loading FC. This might be
technically simpler to implement. However: Expressions that mix tensors living in D=4 and D=!=4 will
not be supported.