(VAR X N M X1 X2)
(RULES 
active(and(tt,X)) -> mark(X)
active(plus(N,0)) -> mark(N)
active(plus(N,s(M))) -> mark(s(plus(N,M)))
mark(and(X1,X2)) -> active(and(mark(X1),X2))
mark(tt) -> active(tt)
mark(plus(X1,X2)) -> active(plus(mark(X1),mark(X2)))
mark(0) -> active(0)
mark(s(X)) -> active(s(mark(X)))
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)
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)
s(mark(X)) -> s(X)
s(active(X)) -> s(X)
)