*Rationals.*
The internal data structure for rational numbers is
`rat(`

. `Num`,`Den`)`Den` is always positive, i.e.
the sign of the rational number is the sign of `Num`. Further,
`Num` and `Den` are relative prime. Note that integer `N`
looks like `rat(`

in this representation. You can
control printing of terms with `N`,1)`user:portray/1`

.

*Partial Evaluation, Compilation.*
Once one has a working solver, it is obvious and attractive to run the
constraints in a clause definition at read time or compile time and
proceed with the answer constraints in place of the original
constraints. This gets you constant folding and in fact the full
algebraic power of the solver applied to the avoidance of computations
at runtime. The mechanism to realize this idea is to use
`dump/3`

for the expansion of `{}/1`

, via the goal and
term expansion hook predicates.

*Asserting with Constraints.*
If you use the database, then the clauses you assert might have
constraints associated with their variables. You should use
`projecting_assert/1`

instead of `assert/1`

in order to ensure
that only the relevant and projected constraints get stored in the
database.

| ?-{A+B=<33}, projecting_assert(test(A,B)).{A+B=<33} | ?-listing(test).test(A, B) :- {A+B=<rat(33,1)} | ?-test(A,B).{A+B=<33}

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