EDIT

import java.util.HashSet;

	/**

	 * Provides the set of type which are applicable as in-references for

	 * the <code>subReferenceType</code> passed to this method:

	 *

	 * The type specific rules are:

	 * <ul>

     *     <li>Article -> Journal</li>

     *     <li>Book -> PrintSeries | Journal<br>(Journal is needed here to cover historic

     *     situations: In Ehrenberg's times (Phycology) some articles (prior to publication in a journal)

     *     were printed and delivered to colleagues and libraries (published preprints). Therefore it necessary to allow these as (small)

     *     books being a part of a Journal.)</li>

     *     <li>BookSection -> Book</li>

     *     <li>InProceedings -> Proceedings</li>

     *     <li>Section -> Article | Book | Thesis | Patent | Report | Webpage | inProceedings</li>

     * </ul>

     * In case the passed <code>subReferenceType</code> matches none of the above rules the returned set will be empty.

     * <p>

     * NOTE: If these constraints are being used in UI contexts, it might be sensible in specific situations to add {@link #Generic} and <code>null</code>

     * to the list in case it was not empty.

     *

	 * @param subReferenceType

	 *     The type of the part for which the possible in-refrence types are to be returned.

	 * @return a set, may be empty, never <code>null</code>

	 */

	public Set<ReferenceType> inReferenceContraints(ReferenceType subReferenceType){

	    Set<ReferenceType> inRefTypes = new HashSet<>();

        if(subReferenceType != null && !subReferenceType.equals(ReferenceType.Generic)){

            if(subReferenceType.isArticle()){

                inRefTypes.add(ReferenceType.Journal);

            } else if (subReferenceType == ReferenceType.BookSection) {

                inRefTypes.add(ReferenceType.Book);

            } else if (subReferenceType.isBook()) {

                inRefTypes.add(ReferenceType.PrintSeries);

                inRefTypes.add(ReferenceType.Journal);

            } else if (subReferenceType == ReferenceType.InProceedings) {

                inRefTypes.add(ReferenceType.Proceedings);

            } else if (subReferenceType == ReferenceType.Section) {

                inRefTypes.add(ReferenceType.Article);

                inRefTypes.add(ReferenceType.Book);

                inRefTypes.add(ReferenceType.Thesis);

                inRefTypes.add(ReferenceType.Patent);

                inRefTypes.add(ReferenceType.Report);

                inRefTypes.add(ReferenceType.WebPage);

                inRefTypes.add(ReferenceType.InProceedings);

            }

        }

        return inRefTypes;

    }