class LetterList:
    # Initialize the empty list, and alphabet of allowed letters
    def __init__(self, letters):
        self.alphabet = "abcdefghijklmnopqrstuvwxyz"
        self.letters = letters

    # Returns the list of letters
    def get_letters(self):
        return self.letters

    # Adds a letter to the list if it is allowed
    # Returns True if the letter was added or False otherwise
    def add_letter(self, letter):
        if len(letter) != 1:
            return False
        if letter.lower() not in self.alphabet:
            return False
        self.letters.append(letter)
        return True

    # Combines all the letters into one string and returns it
    def get_string(self):
        return "".join(self.letters)

    # Sets the allowed alphabet
    def set_alphabet(self, alphabet):
        self.alphabet = alphabet

    # A set method for self.letters
    # Returns True if the input was set or False if it was invalid
    def set_letters(self, letters):
        # Check input validity
        for letter in letters:
            if letter not in self.alphabet:
                return False
        self.letters = letters
        return True