(VAR X Y Z X1 X2) (RULES first(0,X) -> nil first(s(X),cons(Y,Z)) -> cons(Y,n__first(X,activate(Z))) from(X) -> cons(X,n__from(s(X))) first(X1,X2) -> n__first(X1,X2) from(X) -> n__from(X) activate(n__first(X1,X2)) -> first(X1,X2) activate(n__from(X)) -> from(X) activate(X) -> X )