Maxima/Ecl on 32-bit machine cannot evaluate "apply(union, listify({{..}}))"

I haven't figured out the big-oh estimates, but I now mostly understand 
why tree_reduce is fast for this problem:
 
                                                 calls to great
tree_reduce('union,create_list({i},i,1,10^3))        27,364
xreduce('union,create_list({i},i,1,10^3))         2,736,068 
rreduce('append,create_list({i},i,1,10^3))            4,932

For the last, notice that

  (%i50) append(set(a,b), set(b,c));
  (%o50) {a,b,c}


Barton