(VAR M N V1 V2 X )
(STRATEGY CONTEXTSENSITIVE
        (U11 1) 
        (tt ) 
        (U21 1) 
        (s 1) 
        (plus 1 2) 
        (and 1) 
        (isNat ) 
        (0 ) 
)
(RULES 
        U11(tt, N) -> N
        U21(tt, M, N) -> s(plus(N, M))
        and(tt, X) -> X
        isNat(0) -> tt
        isNat(plus(V1, V2)) -> and(isNat(V1), isNat(V2))
        isNat(s(V1)) -> isNat(V1)
        plus(N, 0) -> U11(isNat(N), N)
        plus(N, s(M)) -> U21(and(isNat(M), isNat(N)), M, N)
        
)