TRS:
 {                 a__zeros() -> cons(0(), zeros()),
                 a__U11(tt()) -> tt(),
                 a__U21(tt()) -> tt(),
                 a__U31(tt()) -> tt(),
             a__U41(tt(), V2) -> a__U42(a__isNatIList(V2)),
                 a__U42(tt()) -> tt(),
             a__U51(tt(), V2) -> a__U52(a__isNatList(V2)),
                 a__U52(tt()) -> tt(),
           a__U61(tt(), L, N) -> a__U62(a__isNat(N), L),
              a__U62(tt(), L) -> s(a__length(mark(L))),
                a__isNat(0()) -> tt(),
         a__isNat(length(V1)) -> a__U11(a__isNatList(V1)),
              a__isNat(s(V1)) -> a__U21(a__isNat(V1)),
             a__isNatIList(V) -> a__U31(a__isNatList(V)),
       a__isNatIList(zeros()) -> tt(),
  a__isNatIList(cons(V1, V2)) -> a__U41(a__isNat(V1), V2),
          a__isNatList(nil()) -> tt(),
   a__isNatList(cons(V1, V2)) -> a__U51(a__isNat(V1), V2),
             a__length(nil()) -> 0(),
        a__length(cons(N, L)) -> a__U61(a__isNatList(L), L, N),
                mark(zeros()) -> a__zeros(),
                 mark(U11(X)) -> a__U11(mark(X)),
                 mark(U21(X)) -> a__U21(mark(X)),
                 mark(U31(X)) -> a__U31(mark(X)),
            mark(U41(X1, X2)) -> a__U41(mark(X1), X2),
                 mark(U42(X)) -> a__U42(mark(X)),
          mark(isNatIList(X)) -> a__isNatIList(X),
            mark(U51(X1, X2)) -> a__U51(mark(X1), X2),
                 mark(U52(X)) -> a__U52(mark(X)),
           mark(isNatList(X)) -> a__isNatList(X),
        mark(U61(X1, X2, X3)) -> a__U61(mark(X1), X2, X3),
            mark(U62(X1, X2)) -> a__U62(mark(X1), X2),
               mark(isNat(X)) -> a__isNat(X),
              mark(length(X)) -> a__length(mark(X)),
           mark(cons(X1, X2)) -> cons(mark(X1), X2),
                    mark(0()) -> 0(),
                   mark(tt()) -> tt(),
                   mark(s(X)) -> s(mark(X)),
                  mark(nil()) -> nil(),
                   a__zeros() -> zeros(),
                    a__U11(X) -> U11(X),
                    a__U21(X) -> U21(X),
                    a__U31(X) -> U31(X),
               a__U41(X1, X2) -> U41(X1, X2),
                    a__U42(X) -> U42(X),
             a__isNatIList(X) -> isNatIList(X),
               a__U51(X1, X2) -> U51(X1, X2),
                    a__U52(X) -> U52(X),
              a__isNatList(X) -> isNatList(X),
           a__U61(X1, X2, X3) -> U61(X1, X2, X3),
               a__U62(X1, X2) -> U62(X1, X2),
                  a__isNat(X) -> isNat(X),
                 a__length(X) -> length(X)}
 Fail