code: public static long checkLessLong(
      final long x,
      final String x_name,
      final long in_upper,
      final String upper_name)
    {
      Objects.requireNonNull(x_name, "Value name");
      Objects.requireNonNull(upper_name, "Upper bound name");
  
      if (x < in_upper) {
        return x;
      }
  
      @SuppressWarnings("boxing") final var message =
        String.format("%s (%d) >= %s (%d)", x_name, x, upper_name, in_upper);
  
      throw new RangeCheckException(message);
    }
docs: <p> Assert that {@code x} (named {@code x_name}) is less than {@code
  in_upper} (named {@code upper_name}). </p>
  
  @param x          The checked value
  @param in_upper   The upper bound
  @param x_name     The name of the checked value
  @param upper_name The name of the upper bound
  
  @return x
  
  @since 2.0.0