code: public BDD restrict(final Collection<Literal> restriction) {
      final BDD resBDD = this.factory.build(this.factory.getF().and(restriction));
      return new BDD(this.factory.underlyingKernel().restrict(index(), resBDD.index()), this.factory);
    }
docs: Restricts the BDD.
  @param restriction the restriction
  @return the restricted BDD