def human_readable(solutions):
    """Print letter solution in a human-readable way

    Parameters
    ----------
    solutions : pandas.DataFrame
        Letter draw best solutions, ordered by number of letters

    Returns
    -------
    str
        Human-readable version of `solutions`
    """
    result = ""
    for i, group in solutions.groupby("nb_letters"):
        result = result + str(i) + " letters:" + "\n"
        result = result + " ".join(group["display"]) + "\n\n"
    return result