def contains_repeated_letter(string):
    """
    It contains at least one letter which repeats with exactly one letter between them,
    like xyx, abcdefeghi (efe), or even aaa.
    """

    for letter_number in range(0, len(string) - 2):
        first_letter = string[letter_number]
        third_letter = string[letter_number + 2]

        if first_letter == third_letter:
            return True

    return False