> For the complete documentation index, see [llms.txt](https://docs.moduluszk.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.moduluszk.io/what-follows-from-the-design/a-contract-cannot-diverge-from-its-specification.md).

# A contract cannot diverge from its specification

There is one artifact. The rule the author wrote is the rule the chain enforces, so the failure class where implementation drifts from intent has nothing to divide. Two consequences follow immediately. 

Formal verification stops being a purchase. Elsewhere it is sold as a service layered on top of a manual review, because there remain two artifacts to reconcile. Here it is the default state of the system: every admitted transition arrives with a proof that the stated conditions held. 

Nobody has to trust a description of the contract. The predicate is the terms. A counterparty, an integrator, or a regulator reads the conditions themselves, in the notation rules are naturally stated in, rather than trusting a summary of code they cannot audit. 

What remains the author's problem, and always will, is whether the rules are the right rules. Modulus removes the gap between rule and enforcement; it does not review the rule.