def minus(a, b):
    """
    Returns the assymetrical difference of set 'a' to set 'b' (a minus b).

    In plain english:
        Remove all the items in 'a' from 'b'. Return 'a'. (Order matters.)

    Minus is set_a.difference(set_b). The nomenclature 'difference 
    is not linguistically descriptive (at least to a layman) so the 
    method 'minus' was used, as the meaning of 'minus' conveys the 
    result of the function more properly (once again... at least to 
    the layman).
    """
    return a.difference(b)