function copylist(lst) {
      return mapcar(function (x) { return x; }, lst);
  }
  
  function last(lst) {
      if (null == lst) {
          return null;
      } else if (null == cdr(lst)) {
          return lst;
      } else {
          return last(cdr(lst));
      }
  }

  function append() {
      var lst = null;
      var i = 0;
      for (; i < arguments.length && null == lst; i++) {
          if (null != arguments[i]) {
              lst = copylist(arguments[i]);
          }
      }
      for (; i < arguments.length; i++) {
          if (null != arguments[i]) {
              setcdr(last(lst), copylist(arguments[i]));
          }
      }
      return lst;
  }

  function qsort(lst) {
      if (null == lst) {
          return null;
      } else {
          var pivot = car(lst);
          var nlst = cdr(lst);
          return append(qsort(filter(function (x) { return x < pivot; }, nlst)),
                        list(pivot),
                        qsort(filter(function (x) { return x >= pivot; }, nlst)));
      }
  }
  
  function powerset(lst) {
      if (null == lst) {
          return null;
      } else {
          var first = car(lst);
          var rest  = powerset(cdr(lst));
          return append(list(list(first)),
                        mapcar(function (x) { return append(list(first), x); }, rest),
                        rest);
      }
  }