src/main/java/org/helm/notation2/parser/notation/HELM2Notation.java
public String toHELM2() {
    String output = "";
    /* first section: simple polymer section */
    output += polymerToHELM2() + "$";

    /* second section: connection section */
    output += connectionToHELM2() + "$";

    /* third section: grouping section */
    output += groupingToHELM2() + "$";

    /* fourth section: annotation section */
    output += annotationToHELM2() + "$";

    /* add version number */
    output += "V2.0";

    return output;
  }
public String toHELM2() {
    String output = "";
    /* first section: simple polymer section */
    output += polymerToHELM2() + "$";

    /* second section: connection section */
    output += connectionToHELM2() + "$";

    /* third section: grouping section */
    output += groupingToHELM2() + "$";

    /* fourth section: annotation section */
    output += annotationToHELM2() + "$";

    /* add version number */
    output += "V2.0";

    return output;
  }
method to generate for all sections a HELM2 string

@return HELM2