rascal>PowerSet({1,2,3,4})
set[set[int]]: {
  {4,3},
  {4,2,1},
  {4,3,1},
  {4,2},
  {4,3,2},
  {4,1},
  {4,3,2,1},
  {4},
  {3},
  {2,1},
  {3,1},
  {2},
  {3,2},
  {1},
  {3,2,1},
  {}
}