Copied prerequisite statements

Nothing below searches for a representative of the old ${\mathcal{C}}_3$. X-E/X-F's normalization, X-G's reciprocity pairing, VII-C's word, the IX sharp commutator, and any cone or Enter readout are not inputs.

The general variational treatment of curvature with a scalar prefactor and of nondynamical background breaking provides useful comparison literature SF,BS. The model-specific formulas below are derived in the displayed conventions.