(VAR X X1 X2 X3 Y Z )
(RULES 
        active(and(true, X)) -> mark(X)
        active(and(false, Y)) -> mark(false)
        active(if(true, X, Y)) -> mark(X)
        active(if(false, X, Y)) -> mark(Y)
        active(add(0, X)) -> mark(X)
        active(add(s(X), Y)) -> mark(s(add(X, Y)))
        active(first(0, X)) -> mark(nil)
        active(first(s(X), cons(Y, Z))) -> mark(cons(Y, first(X, Z)))
        active(from(X)) -> mark(cons(X, from(s(X))))
        mark(and(X1, X2)) -> active(and(mark(X1), X2))
        mark(true) -> active(true)
        mark(false) -> active(false)
        mark(if(X1, X2, X3)) -> active(if(mark(X1), X2, X3))
        mark(add(X1, X2)) -> active(add(mark(X1), X2))
        mark(0) -> active(0)
        mark(s(X)) -> active(s(X))
        mark(first(X1, X2)) -> active(first(mark(X1), mark(X2)))
        mark(nil) -> active(nil)
        mark(cons(X1, X2)) -> active(cons(X1, X2))
        mark(from(X)) -> active(from(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)
        if(mark(X1), X2, X3) -> if(X1, X2, X3)
        if(X1, mark(X2), X3) -> if(X1, X2, X3)
        if(X1, X2, mark(X3)) -> if(X1, X2, X3)
        if(active(X1), X2, X3) -> if(X1, X2, X3)
        if(X1, active(X2), X3) -> if(X1, X2, X3)
        if(X1, X2, active(X3)) -> if(X1, X2, X3)
        add(mark(X1), X2) -> add(X1, X2)
        add(X1, mark(X2)) -> add(X1, X2)
        add(active(X1), X2) -> add(X1, X2)
        add(X1, active(X2)) -> add(X1, X2)
        s(mark(X)) -> s(X)
        s(active(X)) -> s(X)
        first(mark(X1), X2) -> first(X1, X2)
        first(X1, mark(X2)) -> first(X1, X2)
        first(active(X1), X2) -> first(X1, X2)
        first(X1, active(X2)) -> first(X1, X2)
        cons(mark(X1), X2) -> cons(X1, X2)
        cons(X1, mark(X2)) -> cons(X1, X2)
        cons(active(X1), X2) -> cons(X1, X2)
        cons(X1, active(X2)) -> cons(X1, X2)
        from(mark(X)) -> from(X)
        from(active(X)) -> from(X)
        
)