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, -(z, s(x)), u)
  f#(s(x), s(y), z, u) -> f#(s(x), -(y, x), z, u)
  f#(s(x), s(y), z, u) -> f#(x, u, z, u)
  rules:
  
  <=(0, y) -> true
  <=(s(x), 0) -> false
  <=(s(x), s(y)) -> <=(x, y)
  -(x, 0) -> x
  -(s(x), s(y)) -> -(x, y)
  f(0, y, 0, u) -> true
  f(0, y, s(z), u) -> false
  f(s(x), 0, z, u) -> f(x, u, -(z, s(x)), u)
  f(s(x), s(y), z, u) -> if(<=(x, y), f(s(x), -(y, x), z, u), f(x, u, z, u))
  if(true, x, y) -> x
  if(false, x, y) -> y
  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, -(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),(1,0),(3,6)]
  Argument Filter: 
  pi(f#/4) = 4
  pi(s/1) = [1]
  pi(-/2) = 1
  pi(0/0) = []
  
  RPO with the following precedence
  precedence(s[1]) = 0
  precedence(0[0]) = 1
  
  precedence(_) = 0
  and the following status
  status(s[1]) = lex
  status(0[0]) = lex
  
  status(_) = lex
  
  problem when orienting DPs
  cannot orient pair f#(s(x), s(y), z, u) -> f#(s(x), -(y, x), z, u) weakly:
  [(f#(s(x), s(y), z, u),0),(s(x),0),(z,6)] >=mu [(f#(s(x), -(y, x), z, u),0),(s(x),0),(z,6)] could not be ensured