def get_missing(index, cmp_index):
    """Get the set of entries that are not in the index and the index that are not in the index .

    Args:
        index (list): Lines on the ffindex
        cmp_index (list): Lines in the other ffindex

    Returns:
        list: List of missing
    """
    missing = set()
    
    index_set = set()
    for entry in index:
        index_set.add(entry[0])
        
    cmp_index_set = set()
    for entry in cmp_index:
        cmp_index_set.add(entry[0])
    
    for key in cmp_index_set:
        if key not in index_set:
            missing.add(key)
    
    return missing