The five rules
Define every symbol. What each variable and constant means is stated before it appears in any equation — no symbol enters an expression undefined.
Specify data types. Every quantity says whether it is a scalar (a single number), a vector (a list of numbers), or a matrix (a grid of numbers) — or a richer type, named just as plainly.
Show explicit operations. Multiplication signs are written out rather than implied by putting letters side by side, so a product can never be confused with a two-letter name.
State dimensions and ranges. Every input and output carries its size limits and its expected number range — a quantity without a range cannot be validated.
Derive before coding. The mathematical steps are written out fully in text before any of them become code. Code implements a derivation the reader has already followed; it never substitutes for one.
How it is used
A convention is summoned into a scope, sandbox style: say mrc — or the plain words “apply the MRC” — and name the document, section, or task. Within that scope the five rules bind completely; they compose with the project’s standing conduct and never override it; the binding releases when the work ends. A document written under the convention says so in one line, so later readers know the rules it was built to.
Where it came from
A governed research instance had an agent describe a mathematical model — and the equations arrived without explanations. The cure was not a one-off correction but a rule-set at the source: the friction was recorded, the five rules were written where standards are written, and the convention now travels the same way every FRACTAL standard travels — adopted by an instance’s own recorded decision, never imposed.
The shipped files: the convention ↓ (the normative source) and mrc.md ↓ (the command that summons it) — both verbatim. The class’s older sibling is the scholarly-source rules.