YES
Input TRS:
      1: flatten(nil()) -> nil()
      2: flatten(unit(x)) -> flatten(x)
      3: flatten(++(x,y)) -> ++(flatten(x),flatten(y))
      4: flatten(++(unit(x),y)) -> ++(flatten(x),flatten(y))
      5: flatten(flatten(x)) -> flatten(x)
      6: rev(nil()) -> nil()
      7: rev(unit(x)) -> unit(x)
      8: rev(++(x,y)) -> ++(rev(y),rev(x))
      9: rev(rev(x)) -> x
      10: ++(x,nil()) -> x
      11: ++(nil(),y) -> y
      12: ++(++(x,y),z) -> ++(x,++(y,z))
Number of strict rules: 12
Direct POLO(bPol) ... removes: 4 1 3 5 10 11 2
      flatten	w: 2 * x1 + 1
      ++	w: x1 + x2 + 2
      unit	w: x1 + 20538
      nil	w: 1
      rev	w: x1
Number of strict rules: 5
Direct POLO(bPol) ... removes: 8 7 6
      flatten	w: 2 * x1 + 1
      ++	w: x1 + x2 + 15922
      unit	w: x1 + 8946
      nil	w: 1
      rev	w: 2 * x1
Number of strict rules: 2
Direct POLO(bPol) ... removes: 9
      flatten	w: 2 * x1 + 1
      ++	w: x1 + x2 + 34509
      unit	w: x1 + 16908
      nil	w: 1
      rev	w: 2 * x1 + 15082
Number of strict rules: 1
Direct POLO(bPol) ... failed.
Uncurrying ... failed.
Dependency Pairs:
     #1: #++(++(x,y),z) -> #++(x,++(y,z))
     #2: #++(++(x,y),z) -> #++(y,z)
Number of SCCs: 1, DPs: 2
  SCC { #1 #2 }
POLO(Sum)... succeeded.
      flatten	w: 0
      ++	w: x1 + x2 + 1
      unit	w: 0
      #++	w: x1
      nil	w: 0
      rev	w: 0
    USABLE RULES: { }
    Removed DPs: #1 #2
Number of SCCs: 0, DPs: 0