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