[ over 0 = iff
      [ 2drop ' [ [ ] ] ]
      done
    dup [] = iff nip done
    1 split rot tuck
    1 - over recurse
    dip [ rot [] ]
    witheach
      [ dip over join
        nested join ]
    nip unrot recurse join ] is comb ( n [ --> [ )

  [ [] swap times
      [ i^ join ]
    comb
    witheach
      [ witheach
          [ echo sp ]
        cr ] ]               is task ( n n -->   )

  3 5 task