code: public static Node getStrictCmml(String mathml) {
          try {
              // get ContentMathML to Strict ContentMathML and finally the abstract CD
              CMMLInfo cmmlInfo = new CMMLInfo(mathml).toStrictCmml();
  
              /*
                Don't use:
                Abstract2CD nicht benutzen! Sobald ein Knoten tatsächlich umbenannt
                wird, verliert dieser Knoten alle Kinder! Stattdessen kann auf dem
                späteren MathNode ein separater toAbstract aufruf erfolgen.
               */
  
              // and finally only get the first apply node of the ContentMathML
              return getFirstApplyNode(cmmlInfo);
          } catch (Exception e) {
              logger.error("failed to get apply node", e);
              return null;
          }
      }
docs: Get the first node of the MathML-Content annotations within a MathML document.
  Before, the MathML document was converted to strict CMML and subsequently also converted
  to display only the abstract variation of the content dictionary.
  
  @param mathml full MathML document
  @return first node of the MathML-Content annotations within a MathML document