def get_unmatched_part(abbr: str, text: str):
    """
    Returns a part of `abbr` that wasn’t directly matched against `str`.
    For example, if abbreviation `poas` is matched against `position`,
    the unmatched part will be `as` since `a` wasn’t found in string stream
    """
    last_pos = 0
    for i, ch in enumerate(abbr):
        last_pos = text.find(ch, last_pos)
        if last_pos == -1:
            return abbr[i:]
        last_pos += 1

    return ''