Keeping the Full Description in View

The procedure

State the full object first. Before borrowing, write down what the borrowed structure is a piece of — for this volume, the metric and the Riemann tensor of full General Relativity, with no linearisation and no effective medium.

Name the proxy at adoption. Not in a footnote and not on review: in the sentence that introduces it. 'We treat the field as a medium with parameters ε_g and μ_g; this is valid to first order in h.'

Write the band as a number, not a word. 'Weak field' is not a band. A stated bound on the neglected term is.

Attach a falsifier. If no measurement could distinguish the proxy from the full object, the proxy is not doing physics, and should be labelled as an aid to thought.

Re-state on every reuse. Labels decay across citations faster than results do. The re-statement is the maintenance.

Why it cannot be automated

Each step requires a judgement about purpose — what the borrowing is for — and purpose is exactly what an optimisation process does not represent. A checker can verify that a status label is present. It cannot verify that the label is the right one, because that requires knowing what the work is trying to be true about. This is the sense in which the requirement is standing: it is not a gate to pass but a practice to keep up, and it is the part of the work that stays human for structural reasons rather than sentimental ones.

The volume ends where it began. The borrowings are good. Riemann's geometry is generous and it lends well. The discipline is only this: return what you borrowed, in the condition you found it, and never mistake the loan for the estate.