docs: public String equationsToString(String prefix, int fractionDigits) {
      DecimalFormat nf = new DecimalFormat();
      nf.setMinimumFractionDigits(fractionDigits);
      nf.setMaximumFractionDigits(fractionDigits);
      nf.setDecimalFormatSymbols(new DecimalFormatSymbols(Locale.US));
      nf.setNegativePrefix("");
      nf.setPositivePrefix("");
      return equationsToString(prefix, nf);
    }