( 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 }
}