def process_synthetic_peptides(cluster):
    """
    Extracts information on identification from the dataset
    PXD004732 which contains reliable identifications of
    synthetic peptides.

    :param cluster: The cluster to process
    :return: A tab-delimited string containing the number of
             synthetic peptide spectra in the cluster, their
             max ratio and the max sequence.
    """
    total_spectra = 0
    sequence_counts = dict()

    for spectrum in cluster.get_spectra():
        # ignore all none synthetic spectra
        if "PXD004732" not in spectrum.get_title():
            continue

        total_spectra += 1

        # spectra from this dataset only contain one psm
        if len(spectrum.psms) != 1:
            raise Exception("Unidentified spectrum from project PXD004732 encountered: " + spectrum.get_title())

        psm = [p for p in spectrum.psms][0]

        if psm.sequence not in sequence_counts:
            sequence_counts[psm.sequence] = 1
        else:
            sequence_counts[psm.sequence] += 1

    # done if no synthetic peptides were found
    if total_spectra == 0:
        return "0\tNA\tNA"

    # get the max count
    max_count = max(sequence_counts.values())

    # get the matching sequences
    max_sequences = [s for s in sequence_counts if sequence_counts[s] == max_count]

    # calculate the ratio
    max_ratio = max_count / total_spectra

    return str(total_spectra) + "\t" + str(max_ratio) + "\t" + ";".join(max_sequences)