(VAR N M X V1 V2 X1 X2 X3)
(RULES 
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))
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)
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)
s(mark(X)) -> s(X)
s(active(X)) -> s(X)
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)
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)
)