def same_at_index(s1: str, s2: str, index: int) -> bool:
    """Return whether s1 and s2 have the same character at the given index.

    This assumes that index is >= 0 and a valid index for both s1 and s2.

    Preconditions:
      - index >= 0
      - len(s1) > index
      - len(s2) > index

    >>> same_at_index('Mario', 'David', 1)
    True
    >>> same_at_index('Hi', 'Bye', 0)
    False
    """
    return s1[index] == s2[index]