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:
  
  top#(mark(X)) -> top#(proper(X))
  top#(ok(X)) -> top#(active(X))
  rules:
  
  active(fst(0, Z)) -> mark(nil)
  active(fst(s(X), cons(Y, Z))) -> mark(cons(Y, fst(X, Z)))
  active(from(X)) -> mark(cons(X, from(s(X))))
  active(add(0, X)) -> mark(X)
  active(add(s(X), Y)) -> mark(s(add(X, Y)))
  active(len(nil)) -> mark(0)
  active(len(cons(X, Z))) -> mark(s(len(Z)))
  active(cons(X1, X2)) -> cons(active(X1), X2)
  active(fst(X1, X2)) -> fst(active(X1), X2)
  active(fst(X1, X2)) -> fst(X1, active(X2))
  active(from(X)) -> from(active(X))
  active(add(X1, X2)) -> add(active(X1), X2)
  active(add(X1, X2)) -> add(X1, active(X2))
  active(len(X)) -> len(active(X))
  add(mark(X1), X2) -> mark(add(X1, X2))
  add(X1, mark(X2)) -> mark(add(X1, X2))
  add(ok(X1), ok(X2)) -> ok(add(X1, X2))
  cons(mark(X1), X2) -> mark(cons(X1, X2))
  cons(ok(X1), ok(X2)) -> ok(cons(X1, X2))
  from(mark(X)) -> mark(from(X))
  from(ok(X)) -> ok(from(X))
  fst(mark(X1), X2) -> mark(fst(X1, X2))
  fst(X1, mark(X2)) -> mark(fst(X1, X2))
  fst(ok(X1), ok(X2)) -> ok(fst(X1, X2))
  len(mark(X)) -> mark(len(X))
  len(ok(X)) -> ok(len(X))
  proper(0) -> ok(0)
  proper(s(X)) -> s(proper(X))
  proper(nil) -> ok(nil)
  proper(cons(X1, X2)) -> cons(proper(X1), proper(X2))
  proper(fst(X1, X2)) -> fst(proper(X1), proper(X2))
  proper(from(X)) -> from(proper(X))
  proper(add(X1, X2)) -> add(proper(X1), proper(X2))
  proper(len(X)) -> len(proper(X))
  s(ok(X)) -> ok(s(X))
  top(mark(X)) -> top(proper(X))
  top(ok(X)) -> top(active(X))
  
   the pairs 
  top#(mark(X)) -> top#(proper(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(top#) = [(epsilon,0),(1,0)]
  polynomial interpretration over naturals with negative constants
  Pol(top#(x_1)) = 1
  Pol(ok(x_1)) = x_1
  Pol(active(x_1)) = x_1
  Pol(mark(x_1)) = 1 + x_1
  Pol(proper(x_1)) = x_1
  Pol(fst(x_1, x_2)) = 1 + x_2 + x_1
  Pol(0) = 0
  Pol(nil) = 0
  Pol(s(x_1)) = 0
  Pol(cons(x_1, x_2)) = x_1
  Pol(from(x_1)) = 1 + x_1
  Pol(add(x_1, x_2)) = 1 + x_2 + x_1
  Pol(len(x_1)) = 1 + x_1
  problem when orienting DPs
  cannot orient pair top#(ok(X)) -> top#(active(X)) weakly:
  [(top#(ok(X)),0),(ok(X),0)] >=mu [(top#(active(X)),0),(active(X),0)] could not be ensured