ceta_eq: termination proof not accepted
1: error below switch to dependency pairs
1.1: error below the dependency graph processor
 1.1.2: error when applying the reduction pair processor with usable rules to remove from the DP problem
  pairs:
  
  rev#(++(x, y)) -> rev#(y)
  rev#(++(x, y)) -> rev#(x)
  rules:
  
  ++(x, nil) -> x
  ++(nil, y) -> y
  ++(++(x, y), z) -> ++(x, ++(y, z))
  flatten(nil) -> nil
  flatten(unit(x)) -> flatten(x)
  flatten(++(x, y)) -> ++(flatten(x), flatten(y))
  flatten(++(unit(x), y)) -> ++(flatten(x), flatten(y))
  flatten(flatten(x)) -> flatten(x)
  rev(nil) -> nil
  rev(unit(x)) -> unit(x)
  rev(++(x, y)) -> ++(rev(y), rev(x))
  rev(rev(x)) -> x
  
   the pairs 
  rev#(++(x, y)) -> rev#(y)
  rev#(++(x, y)) -> rev#(x)
  
  could not apply the generic root reduction pair processor with the following
  SCNP-version with mu = MS and the level mapping defined by 
  pi(rev#) = [(epsilon,0),(1,0)]
  polynomial interpretration over naturals with negative constants
  Pol(rev#(x_1)) = 1
  Pol(++(x_1, x_2)) = 1 + x_2 + x_1
  problem when orienting DPs
  cannot orient pair rev#(++(x, y)) -> rev#(y) strictly:
  [(rev#(++(x, y)),0),(++(x, y),0)] >mu [(rev#(y),0),(y,0)] could not be ensured