( scratchpad ) HS{ 1 2 3 4 } powerset .
HS{
    HS{ 1 2 3 4 }
    HS{ 1 2 }
    HS{ 1 3 }
    HS{ 2 3 }
    HS{ 1 2 3 }
    HS{ 1 4 }
    HS{ 2 4 }
    HS{ }
    HS{ 1 }
    HS{ 2 }
    HS{ 3 }
    HS{ 4 }
    HS{ 1 2 4 }
    HS{ 3 4 }
    HS{ 1 3 4 }
    HS{ 2 3 4 }
}