@Override
  public boolean isValid() {
    for (GrExpression expression : myStringEntries.values()) {
      if (!expression.isValid()) return false;
    }

    for (Couple<GrExpression> entry : myOtherEntries) {
      if (!entry.first.isValid()) return false;
      if (!entry.second.isValid()) return false;
    }

    return true;
  }
@Override
  public boolean isValid()