def is_pangram(sentence):
    letter_flags = 0
    for letter in sentence:
        if letter >= 'a' and letter <= 'z':
            letter_flags |= 1 << ord(letter) - A_LCASE
        elif letter >= 'A' and letter <= 'Z':
            letter_flags |= 1 << ord(letter) - A_UCASE
    return letter_flags == ALL_26_BITS_SET
