code: public Assignment model() {
      if (this.result == UNDEF)
        throw new IllegalStateException("Cannot get a model as long as the formula is not solved.  Call 'solve' first.");
      return this.result != UNSATISFIABLE ? this.createAssignment(this.solver.model()) : null;
    }
docs: Returns the model of the current result.
  @return the model of the current result
  @throws IllegalStateException if the formula is not yet solved