(VAR x y )
(STRATEGY INNERMOST)
(RULES 
        fib(0) -> 0
        fib(s(0)) -> s(0)
        fib(s(s(x))) -> +(fib(s(x)),fib(x))
        +(x,0) -> x
        +(x,s(y)) -> s(+(x,y))
        
)