Reduce this topic to first principles

Strip the central topic of this notebook down to its first principles.

Step 1 — Inventory the assumptions.
List the 6–10 things the sources keep treating as given. State each in plain language.

Step 2 — Classify each assumption.
For every item, decide: is this a physical or logical necessity, a current convention, or a fashion that could change next year? Mark each as Necessity, Convention, or Fashion, and cite the source that reveals which.

Step 3 — Distill the irreducible truths.
After removing every Convention and Fashion, what remains? Write the 3–5 truths that survive, in numbered form, each defensible from first principles alone.

Step 4 — Reason forward.
Using only those first principles — not the conventions you removed — derive 3 non-obvious conclusions. Each conclusion should be something the sources don't quite state but that the principles strictly imply.

If a conclusion contradicts the dominant view in the sources, say so explicitly and explain why the conventions were hiding it.