(0) Obligation:

Generalized rewrite system (where rules with free variables on rhs are allowed):
The TRS R consists of the following rules:

U61(tt) → s(length(L))
and(tt) → X
zeroscons(0)
U11(tt) → U12(isNatList)
U12(tt) → tt
U21(tt) → U22(isNat)
U22(tt) → tt
U31(tt) → U32(isNatList)
U32(tt) → tt
U41(tt) → U42(isNat)
U42(tt) → U43(isNatIList)
U43(tt) → tt
U51(tt) → U52(isNat)
U52(tt) → U53(isNatList)
U53(tt) → tt
isNattt
isNatU11(isNatIListKind)
isNatU21(isNatKind)
isNatIListU31(isNatIListKind)
isNatIListtt
isNatIListU41(and(isNatKind))
isNatIListKindtt
isNatIListKindand(isNatKind)
isNatKindtt
isNatKindisNatIListKind
isNatKindisNatKind
isNatListtt
isNatListU51(and(isNatKind))
length(nil) → 0
length(cons(N)) → U61(and(and(isNatList)))

(1) CritRuleProof (EQUIVALENT transformation)

The rule U61(tt) → s(length(L)) contains free variables in its right-hand side. Hence the TRS is not-terminating.

(2) NO