code: static boolean isFormula(String value, EvaluationWorkbook workbook) {
          try { return FormulaParser.parse(value, (FormulaParsingWorkbook) workbook, 0, 0).length > 1; } // TODO: formulaType and sheet index are 0
          catch (FormulaParseException e) { return false; }
      }
docs: Returns true if value string is formula