code: public Assignment model(final BDD bdd, final Collection<Variable> vars, final boolean defaultValue) {
      final int varBDD = build(this.f.and(vars)).index();
      final int pol = defaultValue ? BDDKernel.BDD_TRUE : BDDKernel.BDD_FALSE;
      final int modelBDD = this.kernel.satOneSet(bdd.index(), varBDD, pol);
      return createAssignment(modelBDD);
    }
docs: Returns an arbitrary model of a given BDD or {@code null} which contains at least the given variables.  If a variable
  is a don't care variable, it will be assigned with the given default value.
  @param bdd          the BDD
  @param vars         the set of variable which has to be contained in the model
  @param defaultValue the default value for don't care variables
  @return an arbitrary model of this BDD