(VAR a x xs y )
(STRATEGY INNERMOST)
(RULES 
        foldl(x,Cons(S(0),xs)) -> foldl(S(x),xs)
        foldl(S(0),Cons(x,xs)) -> foldl(S(x),xs)
        foldr(a,Cons(x,xs)) -> op(x,foldr(a,xs))
        foldr(a,Nil) -> a
        foldl(a,Nil) -> a
        notEmpty(Cons(x,xs)) -> True
        notEmpty(Nil) -> False
        op(x,S(0)) -> S(x)
        op(S(0),y) -> S(y)
        fold(a,xs) -> Cons(foldl(a,xs),Cons(foldr(a,xs),Nil))
        
)