(VAR c l x y ys zs )
(RULES 
        app(x, y) -> helpa(0, plus(length(x), length(y)), x, y)
        plus(x, 0) -> x
        plus(x, s(y)) -> s(plus(x, y))
        length(nil) -> 0
        length(cons(x, y)) -> s(length(y))
        helpa(c, l, ys, zs) -> if(ge(c, l), c, l, ys, zs)
        ge(x, 0) -> true
        ge(0, s(x)) -> false
        ge(s(x), s(y)) -> ge(x, y)
        if(true, c, l, ys, zs) -> nil
        if(false, c, l, ys, zs) -> helpb(c, l, greater(ys, zs), smaller(ys, zs))
        greater(ys, zs) -> helpc(ge(length(ys), length(zs)), ys, zs)
        smaller(ys, zs) -> helpc(ge(length(ys), length(zs)), zs, ys)
        helpc(true, ys, zs) -> ys
        helpc(false, ys, zs) -> zs
        helpb(c, l, cons(y, ys), zs) -> cons(y, helpa(s(c), l, ys, zs))
        
)