def is_valid_input(letter_guessed):
    """
    letter_guessed checks if the argument passed is a valid English letter or not.
    :param letter_guessed: player's char
    :type letter_guessed: string
    :return: True or False, if the player's char is in English
    :rtype: boolean
    """
    is_valid = ((len(letter_guessed) == 1) and (letter_guessed.isalpha()))
    return (is_valid)