User-Defined Constraints

## 1.5 User-Defined Constraints

- Generalised Propagation: propia
- Constraint Handling Rules

### 1.5.1 Generalised Propagation: propia

The predicate infers takes as one argument any user-defined predicate, and as a second argument a form of propagation to be applied to that predicate.
This functionality enables the user to turn any predicate into a constraint [16]. The forms of propagation include finite domains and intervals.

### 1.5.2 Constraint Handling Rules

The user can also specify predicates using rules with guards [9]. They delay until the guard is entailed or disentailed, and then execute or terminate accordingly.
This functionality enables the user to implement constraints in a way that is clearer than directly using the underlying suspend library.