ceta_eq: termination proof not accepted
1: error below switch to dependency pairs
1.1: error below the dependency graph processor
 1.1.1: error when applying the reduction pair processor with usable rules to remove from the DP problem
  pairs:
  
  f#(s(x), 0, z, u) -> f#(x, u, minus(z, s(x)), u)
  f#(s(x), s(y), z, u) -> f#(x, u, z, u)
  rules:
  
  f(0, y, 0, u) -> true
  f(0, y, s(z), u) -> false
  f(s(x), 0, z, u) -> f(x, u, minus(z, s(x)), u)
  f(s(x), s(y), z, u) -> if(le(x, y), f(s(x), minus(y, x), z, u), f(x, u, z, u))
  perfectp(0) -> false
  perfectp(s(x)) -> f(x, s(0), s(x), s(x))
  
   the pairs 
  f#(s(x), 0, z, u) -> f#(x, u, minus(z, s(x)), u)
  f#(s(x), s(y), z, u) -> f#(x, u, z, u)
  
  could not apply the generic root reduction pair processor with the following
  SCNP-version with mu = MS and the level mapping defined by 
  pi(f#) = [(epsilon,0),(1,2)]
  polynomial interpretration over naturals with negative constants
  Pol(f#(x_1, x_2, x_3, x_4)) = x_4
  Pol(s(x_1)) = 1 + x_1
  Pol(0) = 1
  Pol(minus(x_1, x_2)) = x_1
  problem when orienting DPs
  cannot orient pair f#(s(x), 0, z, u) -> f#(x, u, minus(z, s(x)), u) strictly:
  [(f#(s(x), 0, z, u),0),(s(x),2)] >mu [(f#(x, u, minus(z, s(x)), u),0),(x,2)] could not be ensured