code: public static IMolecularFormula getMinimalFormula(MolecularFormulaRange mfRange, IChemObjectBuilder builder) {
          IMolecularFormula formula = builder.newInstance(IMolecularFormula.class);
  
          for (IIsotope isotope : mfRange.isotopes()) {
              formula.addIsotope(isotope, mfRange.getIsotopeCountMin(isotope));
          }
  
          return formula;
      }
docs: Returns the minimal occurrence of the IIsotope into IMolecularFormula
  from this MolelecularFormulaRange.
  
  @param   mfRange The MolecularFormulaRange to analyze
  @return  A IMolecularFormula containing the minimal occurrence of each isotope