@NotNull
  private static String negateBooleanLiteral(GrExpression operand) {
    if (isTrue(operand)) {
      return "false";
    }
    else if (isFalse(operand)) {
      return "true";
    }
    else {
      throw new IllegalStateException(operand.getText());
    }
  }
@NotNull
  private static String negateBooleanLiteral(GrExpression operand)