(VAR N X Y XS) (RULES fib(N) -> sel(N,fib1(s(0),s(0))) fib1(X,Y) -> cons(X) add(0,X) -> X add(s(X),Y) -> s(add(X,Y)) sel(0,cons(X)) -> X sel(s(N),cons(X)) -> sel(N,XS) )