(VAR x y z xs ys)
(RULES
+(0,y) -> y
+(s(x),y) -> s(+(x,y))
++(nil(),ys) -> ys
++(:(x,xs),ys) -> :(x,++(xs,ys))
sum(:(x,nil())) -> :(x,nil())
sum(:(x,:(y,xs))) -> sum(:(+(x,y),xs))
sum(++(xs,:(x,:(y,ys)))) -> sum(++(xs,sum(:(x,:(y,ys)))))

-(x,0) -> x
-(0,s(y)) -> 0
-(s(x),s(y)) -> -(x,y)
quot(0,s(y)) -> 0
quot(s(x),s(y)) -> s(quot(-(x,y),s(y)))
length(nil())-> 0
length(:(x,xs)) -> s(length(xs))
hd(:(x,xs)) -> x
avg(xs) -> quot(hd(sum(xs)),length(xs))
)
(COMMENT Example 4.4 in \cite{O02})