if VERBOSE >= 1:
                print fragment

            # Check whether a reference exists at all
            ref_fn = patient.get_reference_filename(fragment)
            if not os.path.isfile(ref_fn):
                print 'ERROR: reference for fragment', fragment, 'not found!'
                continue
            elif VERBOSE >= 3:
                print 'OK: reference file found'
    
            refseq = SeqIO.read(ref_fn, 'fasta')

            # Check whether the consensus from the first sample is similar to
            # the reference
            for i, sample in enumerate(patient.itersamples()):
                if os.path.isfile(sample.get_consensus_filename(fragment)):
                    sample_init_seq = sample.get_consensus(fragment)
                    if (VERBOSE >= 1) and (i != 0):
                        print 'Consensus from initial sample missing, taking time point',
                        print 'n', i, '(start from zero)'

                    break
            check = check_similarity_initial_sample(refseq, sample_init_seq, fragment,
                                                    VERBOSE=VERBOSE)
            if not check:
                if not use_force:
                    sys.exit()

            # Get the specific fragment for this consensus
            # NOTE: we only recently started hiding the frag spec in the reference name
            if VERBOSE >= 1:
                print fragment

            # Check whether a reference exists at all
            ref_fn = patient.get_reference_filename(fragment)
            if not os.path.isfile(ref_fn):
                print 'ERROR: reference for fragment', fragment, 'not found!'
                continue
            elif VERBOSE >= 3:
                print 'OK: reference file found'

            refseq = SeqIO.read(ref_fn, 'fasta')

            # Check whether the consensus from the first sample is similar to
            # the reference
            for i, sample in enumerate(patient.itersamples()):
                if os.path.isfile(sample.get_consensus_filename(fragment)):
                    sample_init_seq = sample.get_consensus(fragment)
                    if (VERBOSE >= 1) and (i != 0):
                        print 'Consensus from initial sample missing, taking time point',
                        print 'n', i, '(start from zero)'

                    break
            check = check_similarity_initial_sample(refseq,
                                                    sample_init_seq,
                                                    fragment,
                                                    VERBOSE=VERBOSE)
            if not check:
                if not use_force:
                    sys.exit()