(VAR n x xs y )
(STRATEGY INNERMOST)
(RULES 
        qsort(nil) -> nil
        qsort(cons(x,xs)) -> append(qsort(filterlow(x,cons(x,xs))),cons(x,qsort(filterhigh(x,cons(x,xs)))))
        filterlow(n,nil) -> nil
        filterlow(n,cons(x,xs)) -> if1(ge(n,x),n,x,xs)
        if1(true,n,x,xs) -> filterlow(n,xs)
        if1(false,n,x,xs) -> cons(x,filterlow(n,xs))
        filterhigh(n,nil) -> nil
        filterhigh(n,cons(x,xs)) -> if2(ge(x,n),n,x,xs)
        if2(true,n,x,xs) -> filterhigh(n,xs)
        if2(false,n,x,xs) -> cons(x,filterhigh(n,xs))
        ge(x,0) -> true
        ge(0,s(x)) -> false
        ge(s(x),s(y)) -> ge(x,y)
        append(nil,ys) -> ys
        append(cons(x,xs),ys) -> cons(x,append(xs,ys))
        
)