> 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/core-concepts/two-properties-that-fall-out-immediately.md).

# Two properties that fall out immediately

A predicate has a fixed size. It is a statement, and its cost of verification does not depend on how much work satisfying it required off chain. That is why Modulus has nothing to meter and why fee behaviour differs from gas systems; the economics page develops this. 

A predicate is inert. It does not run, so it cannot be interrupted, re-entered, or driven into a state its author never wrote down. The page on what follows from the design lists the bug classes this eliminates.