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:
  
  U11#(mark(X1), X2) -> U11#(X1, X2)
  U11#(X1, mark(X2)) -> U11#(X1, X2)
  U11#(active(X1), X2) -> U11#(X1, X2)
  U11#(X1, active(X2)) -> U11#(X1, X2)
  rules:
  
  U11(mark(X1), X2) -> U11(X1, X2)
  U11(X1, mark(X2)) -> U11(X1, X2)
  U11(active(X1), X2) -> U11(X1, X2)
  U11(X1, active(X2)) -> U11(X1, X2)
  U21(mark(X1), X2, X3) -> U21(X1, X2, X3)
  U21(X1, mark(X2), X3) -> U21(X1, X2, X3)
  U21(X1, X2, mark(X3)) -> U21(X1, X2, X3)
  U21(active(X1), X2, X3) -> U21(X1, X2, X3)
  U21(X1, active(X2), X3) -> U21(X1, X2, X3)
  U21(X1, X2, active(X3)) -> U21(X1, X2, X3)
  active(U11(tt, N)) -> mark(N)
  active(U21(tt, M, N)) -> mark(s(plus(N, M)))
  active(and(tt, X)) -> mark(X)
  active(isNat(0)) -> mark(tt)
  active(isNat(plus(V1, V2))) -> mark(and(isNat(V1), isNat(V2)))
  active(isNat(s(V1))) -> mark(isNat(V1))
  active(plus(N, 0)) -> mark(U11(isNat(N), N))
  active(plus(N, s(M))) -> mark(U21(and(isNat(M), isNat(N)), M, N))
  and(mark(X1), X2) -> and(X1, X2)
  and(X1, mark(X2)) -> and(X1, X2)
  and(active(X1), X2) -> and(X1, X2)
  and(X1, active(X2)) -> and(X1, X2)
  isNat(mark(X)) -> isNat(X)
  isNat(active(X)) -> isNat(X)
  mark(U11(X1, X2)) -> active(U11(mark(X1), X2))
  mark(tt) -> active(tt)
  mark(U21(X1, X2, X3)) -> active(U21(mark(X1), X2, X3))
  mark(s(X)) -> active(s(mark(X)))
  mark(plus(X1, X2)) -> active(plus(mark(X1), mark(X2)))
  mark(and(X1, X2)) -> active(and(mark(X1), X2))
  mark(isNat(X)) -> active(isNat(X))
  mark(0) -> active(0)
  plus(mark(X1), X2) -> plus(X1, X2)
  plus(X1, mark(X2)) -> plus(X1, X2)
  plus(active(X1), X2) -> plus(X1, X2)
  plus(X1, active(X2)) -> plus(X1, X2)
  s(mark(X)) -> s(X)
  s(active(X)) -> s(X)
  
   the pairs 
  U11#(active(X1), X2) -> U11#(X1, X2)
  U11#(X1, active(X2)) -> U11#(X1, X2)
  
  could not apply the generic root reduction pair processor with the following
  SCNP-version with mu = MS and the level mapping defined by 
  pi(U11#) = [(1,3),(2,1)]
  Argument Filter: 
  pi(U11#/2) = 1
  pi(mark/1) = 1
  pi(active/1) = [1]
  
  RPO with the following precedence
  precedence(active[1]) = 0
  
  precedence(_) = 0
  and the following status
  status(active[1]) = lex
  
  status(_) = lex
  
  problem when orienting DPs
  cannot orient pair U11#(mark(X1), X2) -> U11#(X1, X2) weakly:
  [(mark(X1),3),(X2,1)] >=mu [(X1,3),(X2,1)] could not be ensured