The axial parts are the regions a spatial adposition projects onto the Ground's axes, as
behind projects back and under bottom.
- front : AxPart
- back : AxPart
- top : AxPart
- bottom : AxPart
- side : AxPart
- interior : AxPart
- exterior : AxPart
Derives DecidableEq, Repr, Fintype.
Used by SpatialReading