def is_8bit_normal_register(x):
    """ Returns whether the given string x is a "normal" 8 bit register. Those are 8 bit registers
    which belongs to the normal (documented) Z80 instruction set as operands (so a', f', ixh, etc
    are excluded).
    """
    return x.lower() in {'a', 'b', 'c', 'd', 'e', 'i', 'h', 'l'}
