def is_symbol (c):
    """ Checks whether a character is a symbol.

    A symbol is defined as any character that is neither a lowercase letter, uppercase letter or digit.

    Args:
        c (char): The character to check.

    Returns:
        bool: True if the character is a symbol, otherwise false.
    """
    return (not c.islower() and not c.isupper() and not c.isdigit())