Core Concepts

What a predicate is, and why it occupies the slot a contract occupies

A predicate is a statement in first-order logic about a proposed change to state. It is written with the standard connectives and quantifiers: and, or, negation, implication, for-all, there-exists, together with equality and arithmetic comparison over the values involved. It evaluates to true or false over a proposed transition, and nothing else about it exists. There is no method table, no storage layout, no entry point, no execution order. The predicate is the whole contract.