def highlightSubsequence(sequence, x1, x2, start=' [', stop='] '):
    """returns a sequence where the subsequence in [x1, x2[ is placed 
	in bewteen 'start' and 'stop'"""
    seq = list(sequence)
    print(x1, x2 - 1, len(seq))
    seq[x1] = start + seq[x1]
    seq[x2 - 1] = seq[x2 - 1] + stop
    return ''.join(seq)
