procedure power_set (s)
  result := set ()
  if *s = 0
    then insert (result, set ()) # empty set
    else {
      head := set(?s) # take a random element
      # and find powerset of remaining part of set
      tail_pset := power_set (x -- head)
      result ++:= tail_pset # add powerset of remainder to results
      every ps := !tail_pset do # and add head to each powerset from the remainder
        insert (result, ps ++ head)
    }
  return result
end