[ rot dup 0 = iff
      [ drop + ] done
    over 0 = iff
      2drop      done
    over temp put
    dup 1 -
    swap 2swap 1 -
    recurse
    dup temp take +
    again ]           is sudan ( n x y --> f(n) )

  ' [ [ 0 0 0 ]
      [ 1 1 1 ]
      [ 1 3 3 ]
      [ 2 1 1 ]
      [ 2 2 1 ]
      [ 3 1 1 ] ]
  witheach
    [ dup echo say " = "
    do sudan echo cr ]