def display_title(book):
    """Compute the display title of a book."""

    out = book["title"]
    if book.get("subtitle"):
        out += f": {book['subtitle']}"
    if book.get("volume_number") and book.get("fascicle_number"):
        out += f" (vol. {book['volume_number']['raw']}; fas. {book['fascicle_number']['raw']})"
    elif book.get("volume_number"):
        out += f" (vol. {book['volume_number']['raw']})"
    elif book.get("fascicle_number"):
        out += f" (fas. {book['fascicle_number']['raw']})"
    if book.get("volume_title"):
        out += f" / {book['volume_title']}"
    return out