code: public static IMolecularFormulaSet remove(IMolecularFormulaSet formulaSet, IMolecularFormula formulaMin,
              IMolecularFormula formulaMax) {
  
          // prove the correlation between maximum and minimum molecularFormula
          if (!validCorrelation(formulaMin, formulaMax)) return null;
  
          IMolecularFormulaSet newFormulaSet = formulaSet.getBuilder().newInstance(IMolecularFormulaSet.class);
  
          for (IMolecularFormula formula : formulaSet.molecularFormulas()) {
              boolean flagPass = true;
  
              // the formula must contain all element found into the formulaMin
              if (!validCorrelation(formula, formulaMin)) continue;
  
              for (IElement element : MolecularFormulaManipulator.elements(formulaMin)) {
                  int occur = MolecularFormulaManipulator.getElementCount(formula, element);
                  int occurMax = MolecularFormulaManipulator.getElementCount(formulaMax, element);
                  int occurMin = MolecularFormulaManipulator.getElementCount(formulaMin, element);
  
                  if (!(occurMin <= occur) || !(occur <= occurMax)) {
                      flagPass = false;
                      break;
                  }
  
              }
              if (flagPass) // stored if each IElement occurrence is into the limits
                  newFormulaSet.addMolecularFormula(formula);
  
          }
          return newFormulaSet;
      }
docs: Remove all those IMolecularFormula which are not fit theirs IElement
  occurrence into a limits. The limits are given from formulaMax and formulaMin.
  In the minimal IMolecularFormula must contain all those IElement found in the
  minimal IMolecularFormula.
  
  @param formulaSet  IMolecularFormulaSet to look for
  @param formulaMax  A IMolecularFormula which contains the maximal representation of the Elements
  @param formulaMin  A IMolecularFormula which contains the minimal representation of the Elements
  @return            A IMolecularFormulaSet with only the IMolecularFormula which the IElements
  are into the correct occurrence