def combine_strings(one: str, two: str) -> str:
    """Combine strings eliminating duplicate blank lines."""
    if len(one) > 2 and one[-2:] == '\n\n' \
            and len(two) >= 1 and two[0] == '\n':
        # String one has a trailing blank line, and string two has a prefixed
        # blank line.  Strip the duplicate blank line.
        return one + two[1:]
    else:
        return one + two