13. The Interaction Algebra (Flater Appendix C)
This is the contribution beyond the VIM4 2CD and OML, and the reason Flater's note is titled
full tracking of kinds of quantities. Dimensional analysis says torque and
energy share a dimension (\mathrm{M\,L^2\,T^{-2}}), yet they are not the same
kind and not interchangeable. The interaction algebra records which kinds
legitimately combine, with the dimensional product as a coherence side-condition
rather than the definition. It is now realized, sorry-free, in the Interaction
module: the curated product, its division dual, the multiplication–division
round-trip, and the worked torque-versus-energy instance.