List all subsets of the given set.
B = {Lennon, McCartney}
O {}, {Lennon}, {McCartney}
O {}, {Lennon}, {McCartney}, {Lennon, McCartney}
{}, {McCartney}, {Lennon, McCartney}
{ }, {Lennon}, {Lennon, McCartney}
{Lennon}, {McCartney}, {Lennon, McCartney}

please help!